Questions & Answers about Var är det vi ska diskutera rollbesättningen?
Why isn't there a som after Var är det, like there usually is in Vem är det som...?
In cleft questions, the word som is strictly required when the questioned element is the subject of the action (e.g., Vem är det som ska diskutera? - Who is it that will discuss?). Here, the questioned element is a place (Var), and the following clause already has a subject (vi). When the clause already has its own subject, som becomes optional and is very often dropped in everyday Swedish.
What is the difference between asking Var är det vi ska diskutera... and simply Var ska vi diskutera...?
Just like in English ("Where is it that we..." vs. "Where will we..."), the cleft construction adds focus or emphasis. You would use Var är det vi ska... to double-check a location that was already mentioned but forgotten, or to emphasize getting the exact details right. Var ska vi... is a more neutral, out-of-the-blue question.
Why is the word order vi ska diskutera (subject + verb) instead of the inverted ska vi diskutera?
The main clause of this question is actually just Var är det, which uses the expected inverted word order for questions (the verb är comes before the subject det). The rest of the sentence (vi ska diskutera...) functions as a relative clause attached to det. Relative clauses always follow straight word order (Subject + Verb), which is why vi comes before ska.