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