Apex domains cannot have CNAME records.
Question and response
Question
dig novinky.o2.cz. NS
Answer
novinky.o2.cz. 5 NS ns2.silverpop.com.
novinky.o2.cz. 5 NS ns1.silverpop.com.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0