Apex domains cannot have CNAME records.
Question and response
Question
dig sct.de. NS
Answer
sct.de. 5 NS ts1.sct.de.
sct.de. 5 NS ts5.sct.de.
sct.de. 5 NS ns02.telemaxx.net.
sct.de. 5 NS ns03.telemaxx.net.
sct.de. 5 NS ns04.telemaxx.org.
Authority
The response has no authority records.
Additional
ts1.sct.de. 5 A 193.141.27.1
ts5.sct.de. 5 A 193.141.27.6
ns02.telemaxx.net. 5 A 217.160.81.161
ns03.telemaxx.net. 5 A 185.132.35.161
ns04.telemaxx.org. 5 A 185.132.34.161
ts1.sct.de. 5 AAAA 2a04:d140:0:0:0:0:0:1
ts5.sct.de. 5 AAAA 2a04:d140:0:0:0:0:0:3
ns02.telemaxx.net. 5 AAAA 2001:8d8:fe:53:217:160:81:161
ns03.telemaxx.net. 5 AAAA 2607:f1c0:fe:53:185:132:35:161
ns04.telemaxx.org. 5 AAAA 2607:f1c0:fe:53:185:132:34:161
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0