[59nadir]

I think unknown knowns are more easy to spot when teaching newcomers how the system works. Their questions will sometimes be about things we hadn't even considerered (at least in some time) to be the case, but when you have to spell everything out it is indeed the case. In terms of teaching unknown knowns are critical to identify and instead make known knowns so that everyone can end up with a mostly equal playing field.

As an example, there are a lot of unknown knowns that you accumulate over the years in certain lower level languages that need to be spelled out more clearly to someone who is coming at it as a later endeavor. It's entirely possible to spend all your time in a completely managed language nowadays and the concept of the stack, heap, etc., will be largely alien to you. These ideas and their limitations need to be spelled out clearly in order for someone to build the same knowledge base and intuition.

Unknown knowns are essentially endless in nature and extremely hard to find unless you have someone who simply doesn't know to basically fall into traps and guide you toward finding your hidden knowledge.