Apex domains cannot have CNAME records.
Question and response
Question
dig comp.cz. NS
Answer
comp.cz. 1 NS ns2.inecnet.cz.
comp.cz. 1 NS ns.inecnet.cz.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0