"What's 2+2"? In response, the person explains how addition is. "Okay, thanks for that context, but I don't think we ever actually got to the original question - what's 2+2?" The person tells you a story about something cute their kid did when learning addition. "Again, I think we're getting off track - can you please tell me what 2+2 is?"
If they continue long enough, you need to start cutting them off or addressing the issue more directly.
"I've asked four times what 2+2 is, and you've told me several stories about addition but haven't answered the question. Is there some reason you're not able to tell me what 2+2 is?"
Repeat until you either get an answer to the question or an explanation of why the person you're asking can't answer the question.