It appears to originated in the gaming community. I can see many different possible explanations of its original meaning and use:

-We Own the Other Team
-Wow! Loot!

I think that this next origin makes more sense. Hackers in the 80’s would spend hours trying to gain unauthorized root access to a system, and once they did, they would get excited and shout, “Root!” This eventually turned into “W00T!”

A third possible definition, which predates hacking by 700 years, is this first documented use of the term in Chaucer’s “Canterbury Tales”:
“Whos is that faire child, that stondeth yonder?”
“I noot,” quod he, “by God and by Seint John!
A mooder he hath, but fader hath he noon,
That I of woot.” ...
...
“But God woot”

But I am not 100% about what the real origin is. Just some explanations that have been offered.

I like to attribute it to my man Bubb Rubb (youtube video)

not really

that’s only in the morning

@funkdaddy: thanks for posting the Bubb Rubb classic. I’ve been trying to bring back ol’ BR for at least a few years now.

The expression originated in the game World of Warcraft.