Apex domains cannot have CNAME records.
Question and response
Question
dig odn.dk. NS
Answer
odn.dk. 5 NS ns3.dns.services.
odn.dk. 5 NS ns1.dns.services.
odn.dk. 5 NS ns2.dns.services.
Authority
The response has no authority records.
Additional
ns1.dns.services. 5 A 195.242.131.6
ns2.dns.services. 5 A 62.69.152.37
ns3.dns.services. 5 A 185.55.197.53
ns1.dns.services. 5 AAAA 2001:67c:564:ffff:0:0:0:11
ns2.dns.services. 5 AAAA 2a00:1b18:2:3:3:0:0:2
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0