If there's any chance they've heard about a concept, I'll ask if they've heard of it and take them at their word (without comment either way).

And if they're kinda nodding impatiently, I'll wrap up the explanation and move on to the deeper level

At first, people will sometimes be defensive or lie about knowing a topic, but after you establish there's no judgement either way with you I've found people become less hesitant about admitting ignorance and will even want to hear your explanation of something to check their knowledge

I also do the flip side - I pride myself on admitting when I don't know something, so that might play in too