Apex domains cannot have CNAME records.
Question and response
Question
dig stg-cac1-trusted.docebomail.com. NS
Answer
stg-cac1-trusted.docebomail.com. 5 NS ns-1011.awsdns-62.net.
stg-cac1-trusted.docebomail.com. 5 NS ns-2022.awsdns-60.co.uk.
stg-cac1-trusted.docebomail.com. 5 NS ns-235.awsdns-29.com.
stg-cac1-trusted.docebomail.com. 5 NS ns-1329.awsdns-38.org.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0