"What is that fox eating?"
Translation:Co žere ta liška?
No, there is certainly no "JE" in the Czech sentence. The "is" in the English sentence is an English specific part of the continuous form of the verb "is eating", it is really a part of it and you cannot translate it separately. "is eating" = "jí/žere" and also "eats"="jí/žere".
The "to" there is just a possible usage which sometimes accompanies "Co". Co děláš? (What are you doing?) is the same as Co to děláš? It just may help to make the sentence stronger. Also possible: Copak děláš? Copak to děláš?
in engl language there is a timeform that explains that you do it at that moment like "is eating". Why do you use that form here? I cant see a difference to "What eats that fox?" and more important for me, is that timeform also existing in tchec language and how can i see it there? thx for helping me out of the chaos Duoling is sometimes creating for me.