N and King N are different in very essential ways.

N has learned that he was wrong - he tries to be more open minded, and he finds himself wanting to be accepted by humans, trying to learn and trying to fit in a little more with this society. He’s more open and more cheerful.

King N, on the other hand, is arrogant. He believes he is always correct, and sees himself as being superior to other humans. He hates humans. He sees them as evil, a species that corrupts and destroys the lives of his friends. He has a colder attitude, and doesn’t bother trying to fit in. He doesn’t have to - he’s a kind, after all. Why would he want to fit in with the people?

They both like toys, and they both tend to act almost childlike around their Pokemon friends.

… They both also keep their curiosity of the strange trainer they met when Team Plasma started rising - but to King N, it’s… different. He wants to know what caught his attention about someone that didn’t really have anything special, while N just wants to learn more about the first person he considered a friend.