Apex domains cannot have CNAME records.
Question and response
Question
dig work.de. NS
Answer
work.de. 5 NS ns.work.de.
work.de. 5 NS borderzone.work.de.
work.de. 5 NS hulk.work.de.
Authority
The response has no authority records.
Additional
ns.work.de. 5 A 212.12.32.174
hulk.work.de. 5 A 213.158.112.20
borderzone.work.de. 5 A 213.128.138.210
ns.work.de. 5 AAAA 2a00:ea8:200:0:0:0:0:35
hulk.work.de. 5 AAAA 2a00:12d0:1000:500:0:0:0:20
borderzone.work.de. 5 AAAA 2001:868:100:280:0:0:0:4
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0