A girl asks you what you like about her what do i say?

Just be honest and tell her what you like about her. If you guys are going out then tell her how much she means to you & how happy you are to be with her. If you aren't and you're just friends, then that would be kind of awkward so simply list her good qualities i.e. You're a great Flute player or You always make me laugh. That kind of thing.