Apex domains cannot have CNAME records.
Question and response
Question
dig nyborg.dk. NS
Answer
nyborg.dk. 5 NS ns.scannet2.dk.
nyborg.dk. 5 NS ns2.scannet2.dk.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0