Apex domains cannot have CNAME records.
Question and response
Question
dig ntnu.no. NS
Answer
ntnu.no. 5 NS ns2.ntnu.no.
ntnu.no. 5 NS ns1.ntnu.no.
Authority
The response has no authority records.
Additional
ns1.ntnu.no. 5 A 129.241.0.208
ns2.ntnu.no. 5 A 129.241.0.209
ns1.ntnu.no. 5 AAAA 2001:700:300:0:0:0:0:208
ns2.ntnu.no. 5 AAAA 2001:700:300:0:0:0:0:209
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0