[jbattle]

An alternate way to do this (which avoids false negatives cause they don't know the same trivia as you) is to ask them to tell you about a tool/library they are excited about. Or ask them to explain some part of their last project in detail. And then keep asking probing questions to see how deep they can go. You get the same sense of "how deeply does this person actually understand the tools they use" but you dramatically reduce the risk of hitting one of their (rare?) blank spots.

Side benefit #1 is you get a sense of what they think is important

Side benefit #2 is you find out if they can accurately gauge how well they know what they think they know

Side-benefit #3 is you might learn something new!

[jpindar]

This is the kind of thing people in electrical engineering do.