I want to ask my girlfriend to show interest in what I'm interested in.
What kinds of things do you want your girlfriend to show interest in?
I just want her to show interest in the stuff I'm interested in.
It is reasonable to want to have some things in common with your girlfriend so you can talk about the things you both like. But instead of just wanting her to show interest in your likes, you should consider showing interest in hers too. Also, it is fine if people in a relationship like different hobbies and things.
So I should only do whatever she is interested in?
No, I'm only saying that at some point there should be a compromise. You could take turns.