Apex domains cannot have CNAME records.
Question and response
Question
dig quantcom.cz. NS
Answer
quantcom.cz. 5 NS names.dialtelecom.cz.
quantcom.cz. 5 NS sns.dialtelecom.cz.
Authority
The response has no authority records.
Additional
sns.dialtelecom.cz. 5 A 195.250.128.2
names.dialtelecom.cz. 5 A 195.250.136.2
sns.dialtelecom.cz. 5 AAAA 2001:1508:1003:2:0:0:0:4
names.dialtelecom.cz. 5 AAAA 2001:1508:1003:1:0:0:0:2
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0