Apex domains cannot have CNAME records.
Question and response
Question
dig autodns.fairssl.dk. NS
Answer
autodns.fairssl.dk. 5 NS ns-740.awsdns-28.net.
autodns.fairssl.dk. 5 NS ns-1354.awsdns-41.org.
autodns.fairssl.dk. 5 NS ns-1671.awsdns-16.co.uk.
autodns.fairssl.dk. 5 NS ns-132.awsdns-16.com.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0