"Is Kateřina going somewhere?"
Translation:Kateřina někam jde?
The English phrase was quite neutral, without stressing any specific word. If Czech should necessarily stress the last word, then "Kateřina někam jde?" could also be taken as unnatural: "Is Katerina somewhere GOING?" How to convey in Czech the simple English question: "Is Kateřina going somewhere?"?
That would be a funny question, honestly.
The regular question word orders here are: "Jde Kateřina někam?" and "Jde někam Kateřina?"
The order used here, "Kateřina někam jde?" is a surprised question. You either see her leaving or someone just mentioned that she's going. You're confirming with this question.
Your suggestion: "Kateřina jde někam?" would be a question that wants to confirm that she is going somewhere instead of... um, nowhere? A question like "Kateřina jde domů?" (Kateřina is going home?) works fine because you want to know if she's going home as opposed to staying here or going somewhere else. But in this sentence it sounds like "somewhere" is a place and you want to confirm that she's indeed going there.
The only way it could work would be to split it into two sentences: "A Kateřina? Jde někam?" - And Kateřina? Is she going somewhere? - then it becomes a normal question. In casual speech, it's possible to sort of shorten that to "Kateřina, jde někam?" but it's still formally not a single sentence.