My answer to this is easily Breath of The Wild 
especially in terms of geographical knowledge and lore, I really love that game so I did indeed research it alot.
Other than that I’d say I have a lot of knowledge about Final Fantasy 9 though new facts are still surprising me to this day!
@Gamers what about you guys?
I want to say Star Ocean, the Second Story. Over 85 different endings. I played the heck out of that game on two different consoles. But, only Japan has the digital version you can download onto the PS Vita and I’m sooooooooooooooooooooooooo huffy about not having the English version digitized (to be honest, I think they changed all the voice actors and even the updated PSP version annoys me just a bit). I never got the pairings I wanted. Thank goodness for people posting their endings on youtube otherwise I’d never see some of my dream endings.
We’re talking about video games we played/know the most about.
Sally Face, which is funny, because I’ve never played it.
The Sims! Definitely
Animal crossing
Super Monkey Ultra Banana Racing
Or smth like that I forgot the title XD
I recently completed my second playthrough so all the dialogue is pretty fresh in my brain, so I currently have the most knowledge on this game.
In recent memory, The Last of Us Part II is up there for sure. There’s an old game called The Hobbit (a 2003 game based on Tolkien’s book) that I know a lot about as well.
Currently, I’m re-learning how to play LEGO Avengers and learning the game’s “in-game mechanics”.
I’ve heard of those. Mine is definitely Genshin Impact. I think I’m obsessed.