Apex domains cannot have CNAME records.
Question and response
Question
dig ncloud.com. NS
Answer
ncloud.com. 5 NS ns3.naverncp.com.
ncloud.com. 5 NS ns6.naverncp.com.
ncloud.com. 5 NS ns5.naverncp.com.
ncloud.com. 5 NS ns2.naverncp.com.
ncloud.com. 5 NS ns1.naverncp.com.
ncloud.com. 5 NS ns4.naverncp.com.
Authority
The response has no authority records.
Additional
ns1.naverncp.com. 5 A 220.230.123.86
ns2.naverncp.com. 5 A 49.236.143.254
ns3.naverncp.com. 5 A 110.234.41.8
ns4.naverncp.com. 5 A 110.234.4.184
ns5.naverncp.com. 5 A 110.234.57.8
ns6.naverncp.com. 5 A 110.234.33.8
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0