Po: The hardcore can't understand. (Tigress lunges at Po and hugs him, to everyone's shock) Tigress: The hardcore do understand...but I can't watch my friend be killed.
Any of the Po/Tigress moments could qualify, especially in the final half.
There's that private nighttime conversation on the boat. Imagine, Tigress, Po's Resenter in the first film, has grown to become the panda's best friend and confidant of the Five, and maybe the seeds have been laid for something more.
Even more subtly in the film's Super Bowl ad, when you notice that when Po makes his fist excuse, Tigress is smiling with a warm understanding at her friend's effort.
The scene at the end where Po swims up to Tigress at the climax of the film after everyone is hit by Shen's cannon. He whispers her name, holds her hand, and even looks at Shen with a very angry tone. Then, when he pushes her out of harm's way, her hand is still out as if she still wants him to hold it.
Remember, Tigress said that she couldn't feel anything physically because of her Training from Hell she endures (by punching ironwood trees for 20 years). To feel Po's paws just... it just adds more depth to their relationship.
A rather subtle one: In the beginning of the first film, Mr. Ping mentions how he'd always wanted to learn how to make tofu. In the sequel, we see that he has learned to make it and now serves it alongside his noodle soup. In short, Po's success has inspired him to pursue his own dream.
Another subtle one: At the end, Po suggests that he and Mr. Ping cook together, which was the subject of Ping's happy dream in the Holiday Special.
Po offering Shen, the one who slaughtered his own people, a Last-Second Chance. Even though Shen doesn't take it, it still shows a great deal of compassion on Po's part to try and redeem the murderer who orphaned him.
The montage just after Po remembers the probable death of his mother, then to realize things worked out well enough with the love of Mr. Ping creating a home where he was not only loved, but it is in a place where he achieved his most cherished dreams and found his dearest friends, with the last scene of the montage being of Mr. Ping and Baby Po together in his noodle shop.
A small one but Po kissing a bunny toddler on the forehead was quite cute.
Po and Shifu at the end:
Shifu: At last, you have achieved inner peace...and at such a young age.
Po: I had a good teacher.
Shifu's instinct to be Papa Wolf at the first sign of Po in trouble. It just shows that this man has a lot of love to give, since a literal army could not stop him from reaching his surrogate son.
Towards the end after defeating Lord Shen when the remains of his ship, fireworks erupted. It then showed a vague shape of a peacock resembling Lord Shen. It then pans to the Soothsayer, smiling. Maybe Lord Shen did find his peace.
My son is alive.
Ping's adorable flashback to when he first adopted Po, accentuated beautiful by the lightly stringing music. Heck, Ping in general, as he is such a devoted father.
When a couple of indignant customers keep pestering him about where the Dragon Warrior is, Mr. Ping snaps, and goes on a rant about how worried he is about his son. Right when he seems on the verge of crying, Po makes his return. The welcome back hug he gives is maximum heartwarming.
Lord Shen letting the Soothsayer go. For all his evil, he just lets her leave, no strings attatched. And her last words to the man are that she wishes him to find happiness.