Apex domains cannot have CNAME records.
Question and response
Question
dig jos.com.hk. NS
Answer
jos.com.hk. 2 NS ns3.josworld.com.
jos.com.hk. 2 NS ns1.josworld.com.
jos.com.hk. 2 NS ns2.josworld.com.
Authority
The response has no authority records.
Additional
ns1.josworld.com. 1 A 203.189.166.134
ns2.josworld.com. 1 A 203.189.166.135
ns3.josworld.com. 1 A 165.84.176.160
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0