It's from a book I love, Robert Heinlein's Stranger in a Strange Land. The word is the Martian term for fully understanding something.

I believe it is from the book stranger in a strange land. Its meaning is like to deeeeply understand, I think.

You got the original explanation, but grok was taken up by computer nerds way back in the day. It's not merely understanding a thing, in the book or the slang. To grok means to completely wrap your head around the subject, not merely surface level understanding, really feel it down deep.

As to Musk's obsession? He wants to be seen as the cool kid, the smart hacker, the guy who groks what's really going on.

Honestly it's a great name for a search engine or AI. And now he's actively ruining it like everything else he touches.

BTW, Stranger in a Strange Land is an excellent book. I laugh when people call Heinlein a fascist for writing Starship Troopers. "So, how about that hippie book?" Heinlein's books examine various government and economic systems, "What if it worked this way?"

Funny you say that. In Serbia, they say the noise a pig makes is "grok". My wife burst out laughing when she found out the name of Elon's AI.

Imagine some Saudi prince launches an AI called Oink, and then sets up Oinkepedia

I always assumed Grok was chosen to hint as his technology background. For which "grok" is a popular term used for reading and understanding, with code in particular.

trying to be an edgy almost teenager.

grok = caveman?