Apex domains cannot have CNAME records.
Question and response
Question
dig sn. NS
Answer
sn. 5 NS ns1.sonatel.sn.
sn. 5 NS sn.cctld.authdns.ripe.net.
sn. 5 NS ns.ucad.sn.
sn. 5 NS ns-sn.nic.fr.
sn. 5 NS dns-tld.ird.fr.
Authority
The response has no authority records.
Additional
ns.ucad.sn. 99368 A 196.1.95.1
ns1.sonatel.sn. 172794 A 213.154.64.11
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0