Apex domains cannot have CNAME records.
Question and response
Question
dig citibesthk.com. NS
Answer
citibesthk.com. 4 NS ns1.citibesthk.com.
citibesthk.com. 4 NS ns2.citibesthk.com.
Authority
The response has no authority records.
Additional
ns1.citibesthk.com. 4 A 104.250.176.98
ns2.citibesthk.com. 4 A 38.126.208.155
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0