Though I guess right, how would I know this uses "dette" instead of "denne"?
denne is for maculine or feminine nouns, dette is for neuter nouns. But if something is unknown or unspecified, it's referred to as if it was neuter, like "Hva er det?" or "Det regner".
OwO hva er dette?
what have you brought upon this cursed land
Why is "hva er det" wrong? Isn't that the same thing?
dette = this
det = that/it