That will depend on what moment in the story you are referring to. If I can use the entire story, then there are quite a few things that Jonas doesn't like.
War. Jonas doesn't like war, and he doesn't like it when children play games about war. At the end of chapter 17 Jonas sees Fiona and Asher playing a war game. It makes him feel terrible and he starts to cry. The reason is that Jonas knows what war is. He knows what war feels like. He knows it's not something to have fun with in a game.
Jonas also begins to dislike the Sameness. At the beginning of the story, Jonas saw a logic to it. After becoming the Receiver, Jonas has grown to dislike the Sameness and wants to see it end.
By the end of the story Jonas also dislikes (hates) the idea of "releasing" people. That's because he's learned that it's actually murder. It makes sense that Jonas wouldn't like that one. Especially since his brother is supposed to be released.