Apex domains cannot have CNAME records.
Question and response
Question
dig kakao.com. NS
Answer
kakao.com. 5 NS ns2.kakao.com.
kakao.com. 5 NS ns1.kakao.com.
Authority
The response has no authority records.
Additional
ns1.kakao.com. 5 A 113.61.106.5
ns2.kakao.com. 5 A 113.61.107.5
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0