Apex domains cannot have CNAME records.
Question and response
Question
dig lgtel.com. NS
Answer
lgtel.com. 2 NS nis.dacom.co.kr.
lgtel.com. 2 NS ns2.dacom.co.kr.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0