means the same thing as gettin head, gettin dome, etc. Sometimes gettin head is called gettin brains, and this led to "gettin knowledge" because brains=knowledge. Jadakiss used this in "nasty girl" when he said "since she a good girl that attend college, i don't let her gimme brains, i jus let her gimme knowledge".
"Yo, what'd you get into last night"
"Man, you know I had to cop that knowledge"