Apex domains cannot have CNAME records.
Question and response
Question
dig infos.cz. NS
Answer
infos.cz. 5 NS inext.inext.cz.
infos.cz. 5 NS ns.infos.cz.
Authority
The response has no authority records.
Additional
ns.infos.cz. 5 A 46.33.112.42
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0