All examples found in books not of the comic or manga persuasion are here!
Alexis Carew: "You're a girl." Said to Alexis no less than four times by surprised ratings and midshipmen she's introduced to on HMS Merlin (there aren't any other women in the Fringe Fleet). The first time, she answers with mock surprise and the line, "I do believe you're right! Do you think anyone else has noticed?" Then turned on its head when she tries to head it off with Dudgeon, the ship's "carpenter" (essentially chief of maintenance and damage control), by introducing herself with, "I'm a girl."
Dudgeon: Well and I can see that, can't I? I'm not blind.
In the Artemis Fowl series, demons have lived in a different dimension from ours for thousands of years, only learning of human customs and culture through one trashy romance novel, which they take as a sort of Bible. Nº1, a young demon/warlock we first meet in The Last Colony, was particularly interested in the human world, so when he finally gets transported there, he takes great pleasure in pointing out the meaning of human expressions, despite the fact that every other character around him (and the readers) know very well what they mean. It's pointed out that Nº1 does this as a way of coping with stress.
Car magazine AutoWeek frequently features quotes stating the painfully obvious accompanied by a picture of a Captain America lookalike in their "But Wait, There's More..." section.
The Butterfly Kid: where Chester points to Michael Kurland as an example of Whitehead's statement that "It requires an unusual mind to undertake the analysis of the obvious." So he keeps pointing to the obvious everyone has overlooked.
“You’re an alien,” I said. Ten years of university to become Master of the Bleeding Obvious...
Mulenz, a supporting character in the Ciaphas Cain short story The Beguiling, was like this, to Cain's mild annoyance. "No wonder they made him an observer, I thought, nothing gets past this guy."
In The Dilbert Principle, Scott Adams lists Master of the Obvious as one of the roles to take in a meeting. The Master of the Obvious gets lines such as "You need customers in order to have revenue!" and "We want a win-win solution."
In Discworld, the heads of the Feuding Families Selachii and Venturi have to be this whenever they speak to each other due to an edict that they speak only on subjects they couldn't possibly disagree on. Leading to their conversations including phrases like "I see we are standing up."
For some reason, dwarfs tend to be Phrase Catchers for people pointing out that they're dwarfs. In Feet of Clay, Vetinari shows he's not feeling especially clever:
The Patrician stirred, and looked at Cheery through watery red eyes. 'Tell me, young man, are you a policeman?' 'Er... just started, sir.' 'You appear to be of the dwarf persuasion.' Cheery didn't bother to answer. There was no use denying it. Somehow, people could tell if you were a dwarf just by looking at you.
In Duumvirate: Billy & Howard, the twins have vastly different ideas of what is and isn't obvious, occasionally leading to this trope being named.
John Feinstein's book, A Good Walk Spoiled, about the PGA Tour. Scene: Davis Love III, in a tense match late in the Ryder Cup, is approached by his captain Tom Watson:
"We really need this match," [Watson] said ... Love didn't answer right away because the first thought that came into his head wouldn't have sounded very good: "No shit, Tom."
In "The Emperor's New Clothes," the kid who points out that the emperor is nekkid plays this role. Apparently, Andersen took inspiration from his own childhood, where as part of a poor family he saw the procession of the King of Denmark and loudly, indignantly exclaimed "Why, he's nothing more than a human being!".
In "The Nightingale", Andersen opens the story by explaining that "In China, you know, the emperor is a Chinese, and all those about him are Chinamen also."
The Ambassador in The Great Explosion also has this unusual turn of mind. When an officer turns in an estimate of planetary population based on the number of strongholds they see from space, he replies that this says nothing at all about what they CAN'T see. How do you know there aren't some underground? "We haven't seen any." "He says we haven't seen any!"
The Harry Potter books have a few (most are lampshaded in-universe however)
Harry saying "Ghosts are transparent." (What makes this obvious is that he says it in the sixth book, long after ghosts had been introduced; why he said it made sense in context but still got him told "Ah, I see six years of magical education have not been wasted on you.")
Cedric: The cup is a portkey.
The Chinese translation says that Slughorn is saying Ron's name wrong when we can all tell that from the dialogue.
The source of "You can't break an Unbreakable Vow." Harry snarks that he'd worked that much out for himself, and asks what happens if you DO break it. "You die."
Ron: "Hermione, Neville's right... you are a girl...". She lets him live.
One of the things that Ford Prefect had always found hardest to understand about human beings was their habit of continually stating and restating the very, very obvious. As in: "It's a nice day," or "You're very tall," or "So this is it. We're going to die."
Zaphod:(speaking into a phone) Will you please tell us where you are? Marvin: I'm in the car park. Zaphod: The car park? What are you doing there? Marvin: Parking cars, what else does one do in a car park? Zaphod: Okay, hang in there, we'll be right down. (puts down the phone and turns to everyone else) Come on, guys. Marvin's in the car park. Let's get on down. Arthur: What's he doing in a car park? Zaphod: Parking cars, what else? Dumdum....
"It's a cat," I said, winning the Pulitzer Prize for incredible intellect. (and then, after Jax says he wants to keep her): It's a cat. Boy, you couldn't slip anything past me tonight.
Colette disses Ethan for being this trope in Icerigger, for such brilliant demonstrations as remarking "Stuck" after trying and failing to open a jammed door.
The Hunger Games: In Catching Fire, Peeta runs head-first into an invisible force field that stops his heart. CPR revives him, and the first thing he tells Katniss is, "Careful, there's a force field up ahead." He probably had even his enemies laughing with that one.
Justified with Jeeves in Jeeves and Wooster: sometimes he has to be Captain Obvious just to get things through Bertie's head. From the short story "The Ordeal of Young Tuppy" (after Bertie receives a telegram from Tuppy):
The great William Shakespeare brings us this line uttered by Macduff's son in Macbeth: "He has killed me, mother!" Partially explained by the nature of stagecraft in those days, when it was often necessary to make such statements to let the audience know what was going on or what they were supposed to be aware of or understand.
In the second Midnighters book, Madeleine accuses Dess of being one.
Dess: You're a mindcaster. Madeleine: And you have a fine grasp of the obvious.
Dess: You've been mindcasting this to me while I was asleep. Madeleine: I expect that you must earn top marks at school, young lady. There are always rewards for those who state the obvious frequently and with conviction.
Neverwhere : Richard Mayhew. "Oh, you're awake", he tells Door, who is awake.
John Flanagan's Ranger's Apprentice: the Ruins of Gorlan, first in a series. There's a Big Bad monster out there, which is nigh-unstoppable (partly because its eyes could hypnotise). However, it's been established that not only was its mate killed, but that the same natural oil that worked as armour on the beast also made it highly flammable. When the main character, who is being trained in archery by the world's best archer until he can arch with the best, sees his master and other main characters facing the creature, he finally comes up with the ingenious idea to fire a flaming arrow at it. He's hailed as a genius hero, instead of people wondering why nobody had done that right from the beginning.
They didn't know that originally.
Some of Count Olaf's comments in A Series of Unfortunate Events. One example in The Penultimate Peril is when Klaus mentions the 'unfathomable question' in Native Son, Page 581, and Count Olaf points out that that is the five-hundred and eighty-first page.
Enemy Commander: There seems to be a slight problem, my prince. Prince Xizor: So I noticed. Why are your ships blowing up, Commander?
THE Detective, Sherlock Holmes, would consider himself an example of this trope (no shit, indeed), while being the ultimate literary inversion in character and method. In the books he constantly make incredibly obvious observations, admitting that they were "elementary" and "simplicity itself", though of course they were only obvious to Holmes due to his broadness and depth of study - it was still necessary to explain it all to his allies.
The Twits: "To one side there is The Big Dead Tree. It never has any leaves on it because it's dead."
In C. S. Lewis' The Voyage of the Dawn Treader, the entire race of Dufflepuds are prone to this, with such astute observations as water is powerfully wet. Especially the Chief, with things like, "Getting dark now; always does at night." And all the others encourage him constantly.
The Chief: That's a spear, that is. The Others: That it is, Chief, that it is. You couldn't have put it better.
The Chief: Visible we are. And what I say is, when chaps are visible, why, they can see one another. The Others: Ah, there it is, Chief. There's the point. No one's go a clearer head than you. You couldn't have made it plainer.
"She is trapped in the dark for eternal torment. Eternal! That means it will go onforever!"
A book called 100 Things You Aren't Supposed To Know is, well, a list of information that is apparently suppressed from the public knowledge. #37 was "Work kills more people than war," which, if you consider basic mathematics, is like saying "time kills more people than sharks" since there is always, always, always work going on somewhere in the world and war isn't usually happening and nowadays, won't claim explosive numbers of casualties.
The Redwall installment Salamandastron features a scene with The Pigpen begging not to be given a bath; "That stuff's water - it's all wet!"