Apex domains cannot have CNAME records.
Question and response
Question
dig inetadmin.sk. NS
Answer
inetadmin.sk. 5 NS ns.inetadmin.eu.
inetadmin.sk. 5 NS ns.inetadmin.sk.
inetadmin.sk. 5 NS ns.inetadmin.cz.
Authority
The response has no authority records.
Additional
ns.inetadmin.cz. 5 A 109.74.156.29
ns.inetadmin.eu. 5 A 109.74.156.6
ns.inetadmin.sk. 5 A 46.229.225.226
ns.inetadmin.cz. 5 AAAA 2a01:390:1:2:e1b1:2:0:3
ns.inetadmin.sk. 5 AAAA 2a01:390:1:2:e1b1:2:0:2
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0