Apex domains cannot have CNAME records.
Question and response
Question
dig b.akamaiedge.net. NS
Answer
b.akamaiedge.net. 5 NS n5b.akamaiedge.net.
b.akamaiedge.net. 5 NS n3b.akamaiedge.net.
b.akamaiedge.net. 5 NS n0b.akamaiedge.net.
b.akamaiedge.net. 5 NS n7b.akamaiedge.net.
b.akamaiedge.net. 5 NS n2b.akamaiedge.net.
b.akamaiedge.net. 5 NS n4b.akamaiedge.net.
b.akamaiedge.net. 5 NS n1b.akamaiedge.net.
b.akamaiedge.net. 5 NS n6b.akamaiedge.net.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0