RDAP source
https://rdap.nic.cz
port 43: whois.nic.cz
The registry blocks transfers. Often set for valuable or disputed domains.
Signed delegation in place.
WHOIS source
whois.nic.cz
REG-SEZNAM REG-MOJEID REG-MOJEID REG-SEZNAM REG-CZNIC REG-CZNIC
Seznam.cz, a.s. CZ.NIC, z.s.p.o.
Make a direct request at ICANN.