Of Jamaican origin. The literal translation to the standard North American
English dialect would be "you already know" or, "you know it!". Used (to the writers knowledge) mainly in
Toronto, Canada (in its North
American variation) where it has found use among the wider (mostly younger) population and, of course, in its original Jamaican patois dialect everywhere Jamaicans are found (that's globally!).
Used to:
a) Emphasize the validity of a fact (usually stated immediately after the phrase) - e.g. "You done know they're running a scam."
b) Respond affirmatively to a query - e.g. Q: "Are you good for this
money I'm lending you?" A: "You done know"
c) Express
one's assent or agreement - e.g. A: "Boy, it's hot out today!", B: "You done know"
The phrase is also varied to fit the context of the conversation by changing the pronoun used (i.e. "She done know", "They done know", "I done know", etc.)
Jamaican dialect example:
"Yuh done know
di gyal a
lie 'bout 'ar panty size. Everybody know seh 'ar
batty bigga dan dat!" (insert laugh here)
BM