Apex domains cannot have CNAME records.
Question and response
Question
dig cafe24dns.co.kr. NS
Answer
cafe24dns.co.kr. 4 NS ns.cafe24.com.
cafe24dns.co.kr. 4 NS ns1.cafe24.com.
cafe24dns.co.kr. 4 NS ns0.cafe24.com.
cafe24dns.co.kr. 4 NS ns2.cafe24.com.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0