Apex domains cannot have CNAME records.
Question and response
Question
dig linje.dk. NS
Answer
linje.dk. 5 NS lucy.ns.cloudflare.com.
linje.dk. 5 NS stan.ns.cloudflare.com.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0