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