Apex domains cannot have CNAME records.
Question and response
Question
dig emax.net.tw. NS
Answer
emax.net.tw. 5 NS ns2.emax.net.tw.
emax.net.tw. 5 NS ns3.emax.net.tw.
emax.net.tw. 5 NS ns1.emax.net.tw.
Authority
The response has no authority records.
Additional
ns1.emax.net.tw. 5 A 203.217.96.2
ns2.emax.net.tw. 5 A 203.217.96.34
ns3.emax.net.tw. 5 A 203.217.97.1
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0