Apex domains cannot have CNAME records.
Question and response
Question
dig wwi.dk. NS
Answer
wwi.dk. 5 NS ns14.dnsadmin.dk.
wwi.dk. 5 NS ns13.dns-admin.dk.
wwi.dk. 5 NS ns10.dnsadmin.dk.
wwi.dk. 5 NS ns12.dnsadmin.dk.
wwi.dk. 5 NS ns11.dns-admin.dk.
wwi.dk. 5 NS ns15.dns-admin.dk.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0