Apex domains cannot have CNAME records.
Question and response
Question
dig eu.securityeducation.com. NS
Answer
eu.securityeducation.com. 3 NS ns-1611.awsdns-09.co.uk.
eu.securityeducation.com. 3 NS ns-314.awsdns-39.com.
eu.securityeducation.com. 3 NS ns-753.awsdns-30.net.
eu.securityeducation.com. 3 NS ns-1131.awsdns-13.org.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0