Should I power up a Nidoking with cp632 and iv100%?

If you like using Nidoking, sure. But you may regret spending that dust later down the line because you'll probably have other pokemon that do a better job at attacking.

No, there isn't really anything in particular you can use a nidoking effectively in with that moveset. If you have a earthquake one, that would be good for Fire/Electrics, but a Poison only Nidoking has no use in the game so far.

Poison is effective against Exeggutor but you get countered by Psychic moves
Poison is effective against Clefable but again you get countered by Psychic moves
So...whatever poison attacks can exploit it gets countered back.

nice move set, with the base attack power, this is a good attacker

Okay for attacking Snorlax with Lick/Bodyslam, but not for Snorlax with Zen/Hyperbeam.

You shouldn't but you can if you like it. 100% Pokemon's are very rare and special. Moreover, Nidoking Is an decent Pokemon even there will always be a better attacker or defender, he can do both.

No, save your dust - speaking from experience, Nidoking is almost worthless. I made the mistake of powering up a poison jab/earthquake Nidoqueen and I haven't ever used it; I have other pokemon that are much better attackers and defenders.

That said, obviously keep the Nidoking for your collection, since it is 100%.

Save your dust. Maybe the next meta it will be better. I did the same thing as you and powered up my NidoKing a few weeks back to 1800+. I found out he's pretty much useless in defending gyms and has a lot of bad matchups when attacking.

Save your dust for something else.