Apex domains cannot have CNAME records.
Question and response
Question
dig dblc.io. NS
Answer
dblc.io. 5 NS nsa01.corp.dblc.io.
dblc.io. 5 NS nsa02.corp.dblc.io.
Authority
The response has no authority records.
Additional
nsa01.corp.dblc.io. 5 A 79.98.58.55
nsa02.corp.dblc.io. 5 A 185.106.216.15
nsa01.corp.dblc.io. 5 AAAA 2a02:1758:0:cafe:0:0:db1c:53
nsa02.corp.dblc.io. 5 AAAA 2a02:175a:a0:0:0:0:db1c:53
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0