Apex domains cannot have CNAME records.
Question and response
Question
dig pk.ru. NS
Answer
pk.ru. 4 NS ns2.vmts.ru.
pk.ru. 4 NS ns.vmts.ru.
Authority
The response has no authority records.
Additional
ns.vmts.RU. 4 A 212.122.1.2
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0