Apex domains cannot have CNAME records.
Question and response
Question
dig dbc.dk. NS
Answer
dbc.dk. 4 NS sec2.rcode0.net.
dbc.dk. 4 NS sec1.rcode0.net.
Authority
The response has no authority records.
Additional
sec1.rcode0.net. 4 A 192.174.68.100
sec2.rcode0.net. 4 A 176.97.158.100
sec1.rcode0.net. 4 AAAA 2001:67c:1bc:0:0:0:0:100
sec2.rcode0.net. 4 AAAA 2001:67c:10b8:0:0:0:0:100
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0