Apex domains cannot have CNAME records.
Question and response
Question
dig SKNT.RU. NS
Answer
sknt.ru. 3 NS ns4-l2.nic.ru.
sknt.ru. 3 NS skynet.ns.netexpert.ru.
sknt.ru. 3 NS ns.sknt.ru.
sknt.ru. 3 NS ns4-cloud.nic.ru.
sknt.ru. 3 NS ns8-cloud.nic.ru.
sknt.ru. 3 NS ns8-l2.nic.ru.
Authority
The response has no authority records.
Additional
ns.SKNT.RU. 3 A 93.100.1.66
skynet.ns.netexpert.ru. 3 A 94.19.255.12
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0