If Elaine was speaking to King, how come she didn't told King how she died and that Ban didn't killed her?
She did tell King that Ban didn't kill her. When Elaine appeared to King, she outright stated that Ban isn't the person King thinks he is. That pretty much told King that Ban isn't the murderer that King believed Ban to be. As for why she didn't tell King about the Demon, the battle with Guila happening at the time most likely prevented Elaine from telling King the whole story.
Futhermore, Ban doesn't want that King know about the complete deal (otherwise, he would tell King the story himself, before or after that scene). Elaine can know that and she respects it.
How come Ban doesn't want to tell King what happen, I mean he wouldn't believe him but still?
One of the cardinal rules of the order of Seven Deadly Sins as discussed in the Byzel Festival is that they don't talk about their past.
And/Or Ban considers it's his fault because Elaine could have survived if she would have drunk the Fountain herself but she didn't and she saved him instead. Also he could want avoid that King feels guiltier.
How did Hendricksen get the dead demon to the kingdom without anyone noticing?
When the body was found it was in pieces. It's most likely Hendricksen and his knights transported the pieces in separate crates or something and then stitched the whole thing back together in the basement.
They have it hidden in Merlin's castle's basement and Hendricksen said they found it twenty years ago. But they couldn't use that castle until ten years ago. Where did they hid it until then?
Maybe she was really in cahoots with Hendricksen. Maybe they hid it somewhere else until that place was free. Maybe they hid it there without her knowledge. Whatever the reason, it will most likely be revealed later in the manga.
How did one demon manager to escape while the others were still sealed off?
This will be explained in the manga in due time.
Sins Fleeing the Knights
If the Seven Deadly Sins were the strongest order of knights in Liones, then why did they run away from the Holy Knights ten years ago?
It's explained in the flashback. When the Sins discovered Zaratras' corpse, the castle they were in was suddenly surrounded and attacked by all of the knights of the kingdom. They were completely caught off guard and had to run away so they could regroup and figure out later exactly what happened. They maybe called the strongest but having an entire kingdom's worth of Holy Knights maybe too much for them. Note also the current arc in Liones. There was that point wherein three of the Sins were surrounded and only got away thanks to Gowther. After that, they decided to sneak around rather than continue fighting every knight they came across. Then there's Diane and what happened to her.
Diane and High-Heels
If Diane dislike her height so much, why does she wear high heel which make you look taller and how did she get a giant armor for her ten years ago.
Maybe she likes the shoes? I mean there are some women who are sensitive about their weight but aren't so extreme that they deny themselves of something really fulfilling to eat. The same I guess could be said for Diane. Personally, her shoes look more like regular boots rather high heels and it really doesn't matter whether she has high heels or not. For the armor however, it's likely that it was made for her like all the other armors worn by larger knights like Twigo and Kaide, the guy Threader struck in Liones. If armor can be made for those above normal-sized humans, then armor could probably be made for a giant.
Diane and the Portal
How come Diane went first in Oslo portal and not King?
Maybe because King is Oslo's master and was needed to facilitate the teleportation or something? I mean if King went first, would Diane be able to give Oslo the proper instructions to be teleported to Liones? Then again it could be chalked up to Diane being too eager to get to Liones without any real forethought.
Seven Deadly Sins Reputation
Before the whole killing the Great Holy Knight, people seems to show great trust and respect for the Deadly Sins, but they were very dangerous criminal in their past, how much they treated them like knights?
It will be probably be explained in the manga later in more detail on how much they were treated like actual knights. From what is known however, the Sins are a special order of knights made up of conscripted criminals. They are duty bound to serve the kingdom in repentance of their crimes. In doing various deeds for the kingdom such as eliminating vampires and trolls, they are seen as heroes by the populace. However based on Ban mentioning a set of rules during the Byzel festival, it seems like they may have limited freedoms as opposed to regular knights.
Meliodas tied up
Everytime Meliodas wanted to sleep in the same bed as Elizabeth, Hawk tied him up so he doesn't do anything perverted, but Meliodas could break steel easily, why can't he break himself out of it?
He considers it "roleplay" and seems to enjoy it.
Dead or Alive
Elizabeth is one of the keys to release the seal to the demon clan and thats is why Hendricksen needs her (alive). Why then did Guila say in Bryzel that they were ordered to retrieve both princesses dead or alive?
Well maybe she meant Veronica to be dead or alive while Elizabeth remain alive, or it doesn't matter if Elizabeth was alive or not.
Reread chapter 45 where Guila says it and she only mentions one princess, which based on context is obviously Elizabeth. Not sure if it was stated but it seems like they only need Elizabeth's body regardless if she's alive or not.
Diane and Elizabeth shrink
If Diane was using Elizabeth clothes to not be naked, then why didn't she use a piece of clothes like a ribbon so Elizabeth could cover herself and of all places, why her bosom, I mean, shouldn't she told Hawk instead to kept a secret of what happen and give Elizabeth to him?
First off, fanservice. The first few manga covers honestly state that stuff like this was gonna happen. For hiding Elizabeth in Diane's boobs, there apparently was nowhere else Diane could hide her. The waitress uniform apparently has no pockets big enough for a shrunken Elizabeth. For giving Elizabeth something to wear while she was shrunken, well she was covered by the waitress' ribbon beforehand. The ribbon covered Elizabeth while she was carried in Diane's boobs and Diane did give the ribbon with Elizabeth when she handed the latter to Meliodas. Covering the ribbon around Elizabeth beforehand though would be kinda moot. That would require Diane stuffing the ribbon alongside Elizabeth in her boobs. Really unnecessary and more uncomfortable than needed. As for Hawk, he was busy selling beer to the people in the festival. There apparently was no time to hand Elizabeth to him before the reveal. Plus Diane really wanted to keep it as a surprise. Handing Elizabeth to Hawk before it kinda ruins the whole plan since he doesn't have anything where Elizabeth could be hidden. Diane also could have just covered Elizabeth and placed her somewhere else but that defeats the first and main duty of protecting the princess in the first place, especially in such a state. So rather than place Elizabeth on the ground unprotected, might as well just put her in a place that is really close by.
Seven Deadly Sins Strength
If the Seven Deadly Sins are the strongest order of knights in the kingdom, then how come the rest seem to get beaten easily by the Holy Knights with or without their Sacred Gear. And what is holding them back?
In the case of the Sins without their Sacred Weapons, it's because they're not drawing their full strength as explained by King after the Capital of the Dead. Without weapons, they are only drawing a small fraction of what they are capable of. That's why they had a hard time early on. For the Sins with their Sacred Weapons, so far it's because of certain opponents. It's not they're being beaten easily. It's just they're facing opponents that have an advantage over them. With King, it seems to have something to do with Helbram as Gowther stated. Now that he's in Liones, it will probably be addressed especially considering the state Diane is in. With Diane, the only one who proved to be an actual threat was Dreyfus. His power was apparently stronger than her's. There's probably also the fact that she's in the capital and there's innocent people around. With Gowther, it's so far not clear what happened. When he faced Dreyfus, he was dominating over the Great Holy Knight until that shadow appeared. It will probably be explained in the future. The Sins maybe called the strongest but that doesn't mean they don't have weaknesses or can't be beaten.
Diane Sacred Treasure
How Diane lose a Sacred Treasure that is the same size as her?
It will probably be explained in the manga in the future.
Why is Meliodas so annoyed with Diane affection toward him. If he is a pervert like most people say, then why he doesn't enjoy it?
It seems less like Meliodas is annoyed with Diane's affection toward him, and more like he isn't interested in women who aren't Elizabeth and Liz. There seems to be something rather suspicious going on. Both Elizabeth and Liz share the same face and name. There might be a Reincarnation Romance going on.
If King was the Fairy King long time ago and the oldest of the Deadly Sins. Then how come he isn't the leader?
I'm not sure if it was stated that King was the oldest of the Sins but the reason is probably because he isn't the strongest. Meliodas so far has been stated to be the strongest ergo Asskicking Equals Authority.
King Liones Vision
If King Liones can see into the future, why didn't he see the Holy Knight betraying him or his daughter, Veronica, death?
This is kinda a question that frequently gets asked with characters who have such powers. Sadly, the problem with them is that its not always a straightforward answer. He saw the Holy War that was foretold in the prophecies and tried to prevent it. Did his efforts to prevent it fulfilled the prophecy or did he create a completely new timeline in which he didn't forsee what would happen? It'll probably be explained later in the manga in time.
It's explained that his powers have limitations. It doesn't usually give specific details. It's possible that his power did warn him of the coup, but the signs were so vague that he didn't figure out what would happen until it was too late.
Meliodas reaction to Elizabeth
If Elizabeth look just like Liz, then how come Meliodas reacted normally when he first met her?
If by normally you meant by groping her while she was unconscious, then the situation I guess was rather suspicious. Considering that Gowther stated that the Sins had already met Elizabeth when she was a kid, Meliodas might've not been that all too shocked. Also consider their shared history. Meliodas came from and destroyed Danafor. Elizabeth is stated to be from Danafor. Maybe Meliodas knows something about Elizabeth that has yet to be revealed in the manga.
Elizabeth Rusted Armor
When Elizabeth first appear, she was wearing a armor that was twice her size, how was she able to move around with just armor?
Maybe Elizabeth's rusted armor was just that light.
King Fat Form
If it took a lot of energy for King to keep of this form, then how he was able to handle it for five years with the Deadly Sins?
So far it's been stated that King's Fat Form takes alot of energy to maintain that he can't use his other abilities to their fullest. As far as I can remember, that's all he suffers from while in it. There doesn't seem to be a limit to how long he can maintain it. Also note the current chapter with King. If there was a limit, someone should've been extremely tired due to staying in a certain weaker form for a rather long time.
How come Elaine didn't know about King imprisonment for a thousand year for his crime. And what happen to the other Fairies?
Elaine probably didn't know about King's imprisonment for a thousand years because nobody told her like how nobody told King that his sister had died. As for the other fairies, unless they were all killed, what happened to them will probably be explained later in the manga.
Just reread Ban's backstory and Elaine stated herself that due to guarding the Fountain of Youth for several years, she doesn't know what's happening outside the forest.
When Helbram was killed by King and explain the helmet origin, why didn't King take the helmet as a reminder of their old friendship?
King probably didn't take Helbram's helmet because of all the pain associated with it. Helbram did explain earlier that he kept the helmet to remind him of how his curiosity got him and his friends captured.
How come when Liz offer Meliodas sword he refuse it, but when Elizabeth offer him the sword, he finally accept it?
It's explained in the story. Meliodas didn't want the sword originally because he didn't want to hurt people. He only accepts it after Ban tells him to start being serious.
Also, Liz just gave him the sword without explaining why. Elizabeth gave Meliodas a Rousing Speech which made him realize Liz didn't want him to kill, but live.
If Diane feels so ashamed by her height, why does she wear high heels boots?