Apex domains cannot have CNAME records.
Question and response
Question
dig unchk.sn. NS
Answer
unchk.sn. 5 NS dns.ucad.sn.
unchk.sn. 5 NS ns-b.unchk.sn.
unchk.sn. 5 NS ns.unchk.sn.
unchk.sn. 5 NS ns-a.unchk.sn.
Authority
The response has no authority records.
Additional
ns.unchk.sn. 5 A 102.36.136.94
ns.unchk.sn. 5 A 102.36.138.94
ns-a.unchk.sn. 5 A 102.36.138.88
ns-b.unchk.sn. 5 A 41.82.212.204
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0