Apex domains cannot have CNAME records.
Question and response
Question
dig telia.dk. NS
Answer
telia.dk. 5 NS dns49.de.telia.net.
telia.dk. 5 NS dns2.telia.com.
telia.dk. 5 NS dns102.telia.com.
telia.dk. 5 NS dns101.telia.com.
Authority
The response has no authority records.
Additional
dns2.telia.com. 5 A 81.228.10.67
dns49.de.telia.net. 5 A 213.248.77.82
dns49.de.telia.net. 5 AAAA 2001:2030:c000:5:0:0:0:4
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0