Apex domains cannot have CNAME records.
Question and response
Question
dig akamai.com. NS
Answer
akamai.com. 5 NS a1-66.akam.net.
akamai.com. 5 NS a13-66.akam.net.
akamai.com. 5 NS a12-66.akam.net.
akamai.com. 5 NS a3-66.akam.net.
akamai.com. 5 NS a6-66.akam.net.
akamai.com. 5 NS a7-66.akam.net.
akamai.com. 5 NS a11-66.akam.net.
akamai.com. 5 NS a8-66.akam.net.
akamai.com. 5 NS a9-66.akam.net.
akamai.com. 5 NS a5-66.akam.net.
akamai.com. 5 NS a28-66.akam.net.
akamai.com. 5 NS a18-66.akam.net.
akamai.com. 5 NS a16-66.akam.net.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0