1. Brook, a former Royal Guard of an allied Kingdom (most likely Manmayer).
2. Broggy, who listened St. Sommers presenting himself as a Knight of God literally few minutes before.
3. Fisher Tiger, Celestial Dragon's slave for years in Mary Geoise. The poor bastard probably knew Mary Geoise better than Fishmen Island at that point.
4. Loki, who was directly proposed the Knight of God honor by St. Shamrock & Gunko that same day.
5. Sakazuki, Navy Fleet Admiral, the very guy that actually interacts with the top brass of the World Govt. (along with few others like Borsalino and Tensei).
6. Dragon, Supreme Commander of the Revolutionary Army, the man that built his entire excistence on his plan on studying the Celestial Dragons to overthrow them. He even saw the Human Hunt in God Valley.
7. Emporio Ivankov, Dragon't longest ally and subordinate.
8. Not sure what you're pointing at with this last one.
As you can see, all the individuals that know the Knight of God exist have very precise reasons/roles that justify their knolwledge.
But, to be fair, your poor reading comprehension is not new to me, kurwa.