Ask HN: How do you find your unknown unknowns?

Frequently with my dealings with impostor syndrome, I feel like I've built a tower but it is mostly scaffolding rather than solid foundation. Im not an architect so I dont know what I am missing.

Perhaps the best route is to just start from the beginning and slowly fill in the blanks(while also re-learning some things you already know well)

Im wondering if there is some way to discover the missing pieces of the tower and focus studies on those? quiz, app, etc.