Would 'Er det nok?' be OK?
Yes, and it is and was accepted.
Are those sentences always interchangeble?
In the meaning of "Is it enough?", yes.
However, "Holder det?" can also mean "Does it hold?"/"Is it holding?"/"Will it hold?".
Takk for svaret!
Is there a difference between "holder" and "nok"? Thanks for the answer!
I think that Holder is a verb and can't be used as Nok .
Hva med "Rekker det?"
Yes, that works as well. It's a less common alternative.
Is 'Er det holder' also correct?
No, I don't think so. "Holder" is the verb here.
"Er det nok?" would be a possibility I think. In that case "er" is the verb.
Ah, I'd forgotten about the V2 rule. Thank you. :)