Green’s Dictionary of Slang

1. (also do the knob) to hit in the face or head.

1818		Sporting Mag. II. 211: He knobbed his adversary well .
1953		T.A.G. Hungerford Riverslake 26: Look out, Jerry – he’ll do the knob any minute!

2. usu. of a man, to have sexual intercourse.

1993		I. Welsh Trainspotting 312: Ye still knobbin Kelly?
1999		K. Sampson Powder 369: The fucking manager was knobbing the big cheese from the record company.
2005		P. Howard Curious Incident of the Dog in the Nightdress 119: If you must know I knobbed Pikey’s bird!
2015		I. Welsh Decent Ride 326: Easy for that cunt tae say, when eh’s knobbin ma fuckin burd!