Ask for Help with a Trivia Question
This falls into the same realm of asking for general help. The idea is to have the person feel good about his/her knowledge and the help he/she is able to provide to you.
Ask the person for help with something you're pretty sure they would know the answer to. Like say to them, "I have a bet with a friend - what's the next line to the song that goes:
Busted Flat in Baton Rogue, Waiting for a Train,
Feelin' as faded as my jeans ..."
Choose a song the person would be likely to know of course
If the person says they don't know, you can always prod with "I think the song was by Janis Joplin?" and so on. Even if they just keep saying they don't know, thank them and head along your way. It's that contact you're working on, the ability to talk with each other without it being "scary" or unusual.