Why in this word the ending s is not used? This sentence is from J.Cole's song January 28th.
Cole is the hypnotist, control the game whenever he snap(s) That's every track
Welcome to the world of non-standard dialects. While Standard English, whatever that might be taken to mean, requires the use of an -s on third person singular verbs. Not all dialects do, however.
Specifically, this is likely to be a case of African-American Vernacular English, which probably omits that -s more often than it includes it.
Unless you specifically want to be learning AAVE, don't take that sort of song as an example. Indeed, even where they are ostensibly in standard English, poetry and song lyrics often take considerable liberties with grammar and syntax, so they aren't good examples to learn from.