Apex domains cannot have CNAME records.
Question and response
Question
dig z.com. NS
Answer
z.com. 4 NS ns1.cf.gmointernet.jp.
z.com. 4 NS ns2.cf.gmointernet.jp.
Authority
The response has no authority records.
Additional
ns1.cf.gmointernet.jp. 5 A 162.159.10.130
ns2.cf.gmointernet.jp. 5 A 162.159.11.173
ns1.cf.gmointernet.jp. 5 AAAA 2400:cb00:2049:1:0:0:a29f:a82
ns2.cf.gmointernet.jp. 5 AAAA 2400:cb00:2049:1:0:0:a29f:bad
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0