Apex domains cannot have CNAME records.
Question and response
Question
dig uos.net.ua. NS
Answer
uos.net.ua. 4 NS ns2.uos.net.ua.
uos.net.ua. 4 NS ns.uos.net.ua.
uos.net.ua. 4 NS ns.secondary.net.ua.
uos.net.ua. 4 NS ns2.trifle.net.
Authority
The response has no authority records.
Additional
ns.uos.net.ua. 4 A 178.214.192.2
ns2.uos.net.ua. 4 A 178.214.192.22
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0