Apex domains cannot have CNAME records.
Question and response
Question
dig eserver.rs. NS
Answer
eserver.rs. 2 NS ns2.sk.eserver.net.
eserver.rs. 2 NS ns1.sk.eserver.net.
eserver.rs. 2 NS ns4.sk.eserver.net.
eserver.rs. 2 NS ns3.sk.eserver.net.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0