Apex domains cannot have CNAME records.
Question and response
Question
dig tagadab.com. NS
Answer
tagadab.com. 5 NS ns03.tagadab.com.
tagadab.com. 5 NS ns01.tagadab.com.
tagadab.com. 5 NS ns02.tagadab.com.
Authority
The response has no authority records.
Additional
ns01.tagadab.com. 5 A 91.186.2.140
ns02.tagadab.com. 5 A 91.186.2.141
ns03.tagadab.com. 5 A 81.88.54.114
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0