Apex domains cannot have CNAME records.
Question and response
Question
dig dnspartner.de. NS
Answer
dnspartner.de. 5 NS ns2.dnspartner.de.
dnspartner.de. 5 NS ns1.dnspartner.de.
Authority
The response has no authority records.
Additional
ns1.dnspartner.de. 5 A 91.184.32.34
ns2.dnspartner.de. 5 A 178.33.39.66
ns1.dnspartner.de. 5 AAAA 2a01:198:0:1:0:0:0:34
ns2.dnspartner.de. 5 AAAA 2001:41d0:304:200:0:0:0:c92a
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0