Apex domains cannot have CNAME records.
Question and response
Question
dig pccw-hkt.com. NS
Answer
pccw-hkt.com. 4 NS ns5.imsbiz.com.
pccw-hkt.com. 4 NS ns6.imsbiz.com.
Authority
The response has no authority records.
Additional
ns5.imsbiz.com. 4 A 210.87.250.59
ns6.imsbiz.com. 4 A 210.87.253.35
ns5.imsbiz.com. 4 AAAA 2400:c800:5010:1:0:0:0:24
ns6.imsbiz.com. 4 AAAA 2400:c800:5010:1001:0:0:0:13
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0