Of course it's a subdomain. There is no such thing as an official ccTLD called .cz.cc (or .co.cc, .co.tv, .euro.st, .us.tt, .uk.pn, .de.vu, and plenty of other such services)
I very much wonder if trading subdomains is even allowed according to their terms and conditions , because you only borrow them for free in the first place and are not supposed to sell something that's not legally yours. Also, only a fool would pay for this ; many redirection and free subdomain providers cease to exist after a while and then all existing subdomains are gone as well. If you can get a real domain these days for 10 Euro or lower, then why would anyone want to spend more money on a subdomain of which you're not sure if it will continue to exist?!
PS: even if cz.cc were an official extention, prag.cz.cc would still be worthless. In English it's Prague, in Czech language it's Praha. Prag is the German variant, and where's the sense in the German name of the city with .cz.cc as extention? Makes as much sense as for example moscow.us.tt ... Not saying that praha.cz.cc would be worth more than a penny, but terrible subdomain extention and a typo combined??!