Apex domains cannot have CNAME records.
Question and response
Question
dig adminforge.de. NS
Answer
adminforge.de. 4 NS ns.inwx.de.
adminforge.de. 4 NS ns2.inwx.de.
adminforge.de. 4 NS ns3.inwx.eu.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0