Apex domains cannot have CNAME records.
Question and response
Question
dig truhlarstvi-hnedkovsky.com. NS
Answer
truhlarstvi-hnedkovsky.com. 5 NS ns1.truhlarstvi-hnedkovsky.com.
truhlarstvi-hnedkovsky.com. 5 NS ns2.truhlarstvi-hnedkovsky.com.
Authority
The response has no authority records.
Additional
ns1.truhlarstvi-hnedkovsky.com. 5 A 125.253.122.15
ns2.truhlarstvi-hnedkovsky.com. 5 A 125.253.122.18
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0