Do you know any books like the king killer chronicles or harry potter?

Those are very dissimilar books. Although they are both Fantasies and multi-volume, Harry is a Young Adult Urban Fantasy. Its intended audience and the main characters are children. And it takes place (partly at least) in our world.

King Killer is your basic standard fantasy.

You could just go to the library and ask the librarian for help. She can probably help you figure out what kind of book you like. and not only recommend a few but you will be able to leave the library with a few books in your hand.

Or join GoodReads. GoodReads is pretty good at finding similar books and making recommendations.

In the meantime, I'm going to recommend Tamora Pierce. She has written a lot of books so it might be hard to figure out where to start. But you can't go wrong with her first book, Alanna: The First Adventure.

You're on the internet. What's stopping you from googling the words 'books like the King Killer Chronicles'?

A series of unfortunate events, the game of thrones books, lord of the rings