Oh my Knob is a phrase taken from timed where the school would not let you curse openly. The prase its self is a classin word play of "oh my god" but 'God' is replaced with Life 'Knob' to not break that sacred 3rd amendment. 'Knob' is a slag word for dick which id a word that would not be allowed on school grounds except for lil richard. So what your really saying is "OH MY DICK" but with a clean word for dick.
"Hey billy do your math homework?"
"Oh my knob i forgot!"