Apex domains cannot have CNAME records.
Question and response
Question
dig checon.de. NS
Answer
checon.de. 4 NS ns6.checon.de.
checon.de. 4 NS b.ns14.net.
checon.de. 4 NS ns.ipn.de.
checon.de. 4 NS ns.checon.net.
Authority
The response has no authority records.
Additional
ns.ipn.de. 4 A 193.96.188.100
ns6.checon.de. 4 A 89.146.248.4
ns6.checon.de. 4 AAAA 2a01:130:2000:118:89:146:248:4
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0