Apex domains cannot have CNAME records.
Question and response
Question
dig wh.cloud.z.com. NS
Answer
wh.cloud.z.com. 5 NS ns-a1.zc-dns.com.
wh.cloud.z.com. 5 NS ns-a3.zc-dns.org.
wh.cloud.z.com. 5 NS ns-a2.zc-dns.net.
wh.cloud.z.com. 5 NS ns-a6.cloud.z.com.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0