Apex domains cannot have CNAME records.
Question and response
Question
dig octor.com. NS
Answer
octor.com. 1 NS dns.apol.com.tw.
octor.com. 1 NS dns.octor.com.
Authority
The response has no authority records.
Additional
dns.apol.com.tw. 1 A 61.20.46.204
dns.octor.com. 1 A 61.20.46.203
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0