whats the best part of the head to hit?

( sorry if is hard to understand, english is not my native language)

so i always think about how i could defend myself in a robbery/fight/bully situation, so i watched some self defense videos, i know some techniques now, but im always asked about the weakest point of the head, im not talking about the the face (chin, eyes, nose) im talking about the skull, I studied some bones and their names but I still don't know which one would be the most effective to hit in a fight