Apex domains cannot have CNAME records.
Question and response
Question
dig hkt.com. NS
Answer
hkt.com. 5 NS ns2.hkt.com.
hkt.com. 5 NS ns3.hkt.com.
hkt.com. 5 NS ns4.hkt.com.
hkt.com. 5 NS ns1.hkt.com.
Authority
The response has no authority records.
Additional
ns1.hkt.com. 5 A 202.164.27.100
ns2.hkt.com. 5 A 202.164.27.100
ns3.hkt.com. 5 A 203.29.222.100
ns4.hkt.com. 5 A 203.29.222.100
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0