Apex domains cannot have CNAME records.
Question and response
Question
dig niks.su. NS
Answer
niks.su. 4 NS ns2.runnet.ru.
niks.su. 4 NS ns.runnet.ru.
Authority
The response has no authority records.
Additional
ns.runnet.ru. 4 A 194.85.32.18
ns2.runnet.ru. 4 A 185.220.193.99
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0