Apex domains cannot have CNAME records.
Question and response
Question
dig dpgapi.dk. NS
Answer
dpgapi.dk. 5 NS ns01.one.com.
dpgapi.dk. 5 NS ns02.one.com.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0