Apex domains cannot have CNAME records.
Question and response
Question
dig hkn.cloud. NS
Answer
hkn.cloud. 5 NS neos.hkn.de.
hkn.cloud. 5 NS sns02.hkn.de.
Authority
The response has no authority records.
Additional
neos.hkn.de. 5 A 212.46.104.104
sns02.hkn.de. 5 A 213.9.97.198
neos.hkn.de. 5 AAAA 2a02:4c00:0:4010:0:0:0:2
sns02.hkn.de. 5 AAAA 2a02:4c00:0:4011:0:0:0:2
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0