Apex domains cannot have CNAME records.
Question and response
Question
dig wayf.dk. NS
Answer
wayf.dk. 5 NS ns1.sdu.dk.
wayf.dk. 5 NS backup-server.nordu.net.
wayf.dk. 5 NS server.nordu.net.
wayf.dk. 5 NS ns2.sdu.dk.
Authority
The response has no authority records.
Additional
ns1.sdu.dk. 5 A 130.225.155.136
ns2.sdu.dk. 5 A 130.225.155.148
server.nordu.net. 5 A 193.10.252.19
backup-server.nordu.net. 5 A 193.10.252.66
server.nordu.net. 5 AAAA 2001:948:4:2:0:0:0:19
backup-server.nordu.net. 5 AAAA 2001:948:4:1:0:0:0:66
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0