Apex domains cannot have CNAME records.
Question and response
Question
dig ent-apse2-trusted.docebomail.com. NS
Answer
ent-apse2-trusted.docebomail.com. 5 NS ns-1161.awsdns-17.org.
ent-apse2-trusted.docebomail.com. 5 NS ns-244.awsdns-30.com.
ent-apse2-trusted.docebomail.com. 5 NS ns-621.awsdns-13.net.
ent-apse2-trusted.docebomail.com. 5 NS ns-1981.awsdns-55.co.uk.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0