Apex domains cannot have CNAME records.
Question and response
Question
dig 47.78.clients.your-server.de. NS
Answer
47.78.clients.your-server.de. 5 NS ns.second-ns.com.
47.78.clients.your-server.de. 5 NS ns1.your-server.de.
47.78.clients.your-server.de. 5 NS ns3.second-ns.de.
Authority
The response has no authority records.
Additional
ns1.your-server.de. 5 A 213.133.100.102
ns1.your-server.de. 5 AAAA 2a01:4f8:0:1:0:0:5ddc:1
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0