At the moment I have a Nidoran♂ with the egg moves head smash and sucker punch.
Now, I have a male slowpoke with the egg moves amnesia and confusion.
How do I get a Nidoran♂ with all 4 of the egg moves listed?
There is only one way you can get that entire moveset onto a nidoran male. you need to get a male smeargle and sketch all four of the moves you want and then breed with a nidoran female.
The closest you can get without using smeargle is you can use a girafarig to get amnesia/confusion/sucker punch.