Apex domains cannot have CNAME records.
Question and response
Question
dig stofanet.dk. NS
Answer
stofanet.dk. 1 NS dom.ns.cloudflare.com.
stofanet.dk. 1 NS isabel.ns.cloudflare.com.
Authority
The response has no authority records.
Additional
dom.ns.cloudflare.com. 3 A 108.162.193.157
dom.ns.cloudflare.com. 3 A 172.64.33.157
dom.ns.cloudflare.com. 3 A 173.245.59.157
isabel.ns.cloudflare.com. 3 A 108.162.194.104
isabel.ns.cloudflare.com. 3 A 162.159.38.104
isabel.ns.cloudflare.com. 3 A 172.64.34.104
dom.ns.cloudflare.com. 3 AAAA 2606:4700:58:0:0:0:adf5:3b9d
dom.ns.cloudflare.com. 3 AAAA 2803:f800:50:0:0:0:6ca2:c19d
dom.ns.cloudflare.com. 3 AAAA 2a06:98c1:50:0:0:0:ac40:219d
isabel.ns.cloudflare.com. 3 AAAA 2606:4700:50:0:0:0:a29f:2668
isabel.ns.cloudflare.com. 3 AAAA 2803:f800:50:0:0:0:6ca2:c268
isabel.ns.cloudflare.com. 3 AAAA 2a06:98c1:50:0:0:0:ac40:2268
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0