Apex domains cannot have CNAME records.
Question and response
Question
dig sentoo.sn. NS
Answer
sentoo.sn. 5 NS ns1.sonatel.sn.
sentoo.sn. 5 NS ns2.sonatel.sn.
Authority
The response has no authority records.
Additional
ns1.sonatel.sn. 5 A 213.154.64.11
ns2.sonatel.sn. 5 A 41.208.148.68
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0