Apex domains cannot have CNAME records.
Question and response
Question
dig awsdns-28.com. NS
Answer
awsdns-28.com. 5 NS g-ns-604.awsdns-28.com.
awsdns-28.com. 5 NS g-ns-29.awsdns-28.com.
awsdns-28.com. 5 NS g-ns-1756.awsdns-28.com.
awsdns-28.com. 5 NS g-ns-1180.awsdns-28.com.
Authority
The response has no authority records.
Additional
g-ns-29.awsdns-28.com. 5 A 205.251.192.29
g-ns-604.awsdns-28.com. 5 A 205.251.194.92
g-ns-1180.awsdns-28.com. 5 A 205.251.196.156
g-ns-1756.awsdns-28.com. 5 A 205.251.198.220
g-ns-29.awsdns-28.com. 5 AAAA 2600:9000:5300:1d00:0:0:0:1
g-ns-604.awsdns-28.com. 5 AAAA 2600:9000:5302:5c00:0:0:0:1
g-ns-1180.awsdns-28.com. 5 AAAA 2600:9000:5304:9c00:0:0:0:1
g-ns-1756.awsdns-28.com. 5 AAAA 2600:9000:5306:dc00:0:0:0:1
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0