Apex domains cannot have CNAME records.
Question and response
Question
dig kro.kr. NS
Answer
kro.kr. 5 NS 2.ns.dnsze.com.
kro.kr. 5 NS 1.ns.dnsze.com.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0