Perhaps our disagreement is about what you consider to be knowledge?
I share some of my son's obsessively inquisitive traits. I can't recall a topic in recent years where I haven't been able to go down the rabbit hole a scratch that itch to investigate and learn.
I think this graphic is helpful.
I would suggest that the vast majority of the area of that diagram is readily accessible on the internet. Of course, you might need years of study to recognise it and understand it, but it is likely there. The central core area is very well represented.
So if we are talking about what is not accessible via the internet, I'd ask more explicitly - what knowledge do you mean?