You could ask questions they can't easily find the answers to on Google.
Questions like
- what do you think about decentralization?
- do you believe in everyone running his/her node?
- Do you like the new Facebook coin?
- why do you like/dislike Facebook coin?
If you are very informed and idealistic about blockchain/cryptocurrency, you will be able to spot the wolves in sheep clothing, spammers, scammers, trolls etc
I like 2 of those questions. Somebody who's new and getting into Bitcoin may not answer the nodes question.