Apex domains cannot have CNAME records.
Question and response
Question
dig g.apple.com. NS
Answer
g.apple.com. 5 NS ns1.g.aaplimg.com.
g.apple.com. 5 NS ns3.g.aaplimg.com.
g.apple.com. 5 NS b.gslb.aaplimg.com.
g.apple.com. 5 NS ns4.g.aaplimg.com.
g.apple.com. 5 NS a.gslb.aaplimg.com.
g.apple.com. 5 NS ns2.g.aaplimg.com.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0