I know a direct train exists (it was answered here). I tried to buy it via the polish rail and via the Czech rail but without success. How can I buy an electronic ticket for this connection?
I have been looking for all possible options and luckily I could find something. Please double check but I notice this site:
You can book your ticket and it should cost 72.40 euros and 8 hours+ travel time. From Kwakow to Prague. On this site you can change the language settings to UK English. Please note that if you do that the price will be quoted in Pound Sterling and that not all destinations are available. Only the most common.
There is a night train operated by flag carriers PKP Intercity and České dráhy (ČD / Czech Railways). That is available for booking at www.intercity.pl or at station.
LEO Express runs buses across border connecting to their trains to Prague. You may want to book that trip online at www.le.cz.
The same model (bus + train) uses RegioJet, and sells online at jizdenky.regiojet.cz