Apex domains cannot have CNAME records.
Question and response
Question
dig lgtelecom.co.kr. NS
Answer
lgtelecom.co.kr. 4 NS nis.dacom.co.kr.
lgtelecom.co.kr. 4 NS ns2.dacom.co.kr.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0