I asked a friend of mine what hobbies they liked. One was photography. What impressive question can I go back with to make a conversation? I know nothing about photography
If you know nothing about photography, you should not ask "impressive questions". This can only backfire.
The obvious question is to ask what the photographs the person makes are about.
With regard to "impressive questions", this will likely end like the apocryphal story about Ernest Hemingway asking a photographer he admired "I just love your work. What kind of camera do you use?" to which the photographer responded with "And I am a great fan of your writings. What typewriter do you use?".