Apex domains cannot have CNAME records.
Question and response
Question
dig SN.RU. NS
Answer
SN.RU. 4 NS ns6.salenames.RU.
SN.RU. 4 NS ns5.salenames.RU.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0