Apex domains cannot have CNAME records.
Question and response
Question
dig rnids.RS. NS
Answer
rnids.RS. 5 NS odisej.telekom.RS.
rnids.RS. 5 NS nsu.dnsnode.net.
rnids.RS. 5 NS nsp.dnsnode.net.
rnids.RS. 5 NS ns1.rnids.RS.
rnids.RS. 5 NS ns2.rnids.RS.
rnids.RS. 5 NS nordic1.dnsnode.net.
Authority
The response has no authority records.
Additional
ns1.rnids.rs. 5 A 91.199.17.59
ns2.rnids.rs. 5 A 91.199.17.60
ns1.rnids.rs. 5 AAAA 2001:67c:69c:0:0:0:0:59
ns2.rnids.rs. 5 AAAA 2001:67c:69c:0:0:0:0:60
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0