Know Your Customer Kyc

Recently one of my friends told me that there is distinct difference between 'know of something' and 'know about something' expressions. Moreover, If you know about a subject, you have studied it or taken an interest in it, and understand part or all of it. In related context, Why do you think that He doesn't know him from his schooldays means that he does know him? It would only have that sense if you added something like In fact, he first met him at university. Research indicates, For a non-native speaker like me, I am always wondering how to use you know correctly, as in the following sentence: Alright, well, for example, like on Saturdays, y’know, what I liked to do. These findings regarding Know Your Customer Kyc provide comprehensive context for understanding this subject.