If you gotta ask, you can't afford it.

(noun) A successful type of theft which results in an acceptable, impressive and rewarding payday for the protagonist.

if you dont know what it is you probably cant afford it

To get head while still asleep.

recieving head while sleeping

If you don't know. You can't afford it.

A Z Job is were you are recieving a blow job where the giver of the blow job is sleeping, also refered to as catching some zzz's, therefore a z job