How do you say Nicholas in Spanish?

People usually do not translate proper nouns, so if a person's name is "Nick", this will remain the same. The Spanish equivalent of Nicholas, the longform name of which Nick is nickname, is Nicolas.

If you mean "nick" as in a slight scrape or small cut, the verb is "entallar" or "hacer muescas" and the noun is "entalladura" or "muesca".