Apex domains cannot have CNAME records.
Question and response
Question
dig knownhost.com. NS
Answer
knownhost.com. 5 NS cns1.knownhost.com.
knownhost.com. 5 NS cns2.knownhost.com.
Authority
The response has no authority records.
Additional
cns1.knownhost.com. 5 A 162.159.8.79
cns2.knownhost.com. 5 A 162.159.9.126
cns1.knownhost.com. 5 AAAA 2400:cb00:2049:1:0:0:a29f:84f
cns2.knownhost.com. 5 AAAA 2400:cb00:2049:1:0:0:a29f:97e
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0