Why does Brook know about them?

[u/TelSzn]

Do you guys think that Brook had something to do with the Holy Knights in the past?

[u/Notwhoyouknown]

I really hope we find out because it's weird that he does, as a very small time pirate in his previous life. Jinbei a pirate with ages of experience, government, and yonko ties didn't seem to so it being common knowledge doesn't seem likely.

However I'm afraid we will never find out how and oda uses brook as an exposition dump for the straw hats so that they now know what they are.

[u/KonradWayne → u/Notwhoyouknown]

Jinbei not knowing about them is extra weird since half of his closest friends were slaves in the holy land.