Apex domains cannot have CNAME records.
Question and response
Question
dig pf.uns.ac.rs. NS
Answer
pf.uns.ac.rs. 4 NS ns2.loopia.se.
pf.uns.ac.rs. 4 NS ns1.loopia.se.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0