Apex domains cannot have CNAME records.
Question and response
Question
dig gcos.dk. NS
Answer
gcos.dk. 5 NS auth01.t26.dk.
gcos.dk. 5 NS auth02.t26.dk.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0