Gunkeren means that something is another kind of cool, the best way to explain it in English would be to compare it to awesome.
Gunkeren is a word that mostly teenagers use, usually they will be in the meme/gaming community.

Gunkeren, an alternative to nice. Usually it would be used in a setting which includes alcohol, skating, and anything you would consider gnarly. A term often used by frat boys and skaters in Denmark.