Apex domains cannot have CNAME records.
Question and response
Question
dig joboo.de. NS
Answer
joboo.de. 4 NS ns-997.awsdns-60.net.
joboo.de. 4 NS ns-1036.awsdns-01.org.
joboo.de. 4 NS ns-1880.awsdns-43.co.uk.
joboo.de. 4 NS ns-400.awsdns-50.com.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0