I think you can quickly get a sense of depth, potential, curiosity, and passion if you can get them talking about quirks and their opinions on those quirks.
For example, if someone says that they once attached a debugger to the JVM to confirm a pathological issue arising from benign looking Java code and found that the JIT compiler falls apart when a certain construct is used, I’m probably going to hire that person, even if we have no Java code in the company - assuming I can also confirm that they are productive and don’t just waste time going down deep rabbit holes.