Apex domains cannot have CNAME records.
Question and response
Question
dig vw-mms.de. NS
Answer
vw-mms.de. 5 NS ns3.volkswagen.de.
vw-mms.de. 5 NS ns4.volkswagen.de.
vw-mms.de. 5 NS ns1.volkswagen.de.
vw-mms.de. 5 NS ns2.volkswagen.de.
Authority
The response has no authority records.
Additional
ns1.volkswagen.de. 5 A 198.51.44.1
ns2.volkswagen.de. 5 A 198.51.45.1
ns3.volkswagen.de. 5 A 198.51.44.65
ns4.volkswagen.de. 5 A 198.51.45.65
ns1.volkswagen.de. 5 AAAA 2620:4d:4000:6259:7:1:0:1
ns2.volkswagen.de. 5 AAAA 2a00:edc0:6259:7:1:0:0:2
ns3.volkswagen.de. 5 AAAA 2620:4d:4000:6259:7:1:0:3
ns4.volkswagen.de. 5 AAAA 2a00:edc0:6259:7:1:0:0:4
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0