"What is the most popular movie today?"
Translation:Qual é o filme mais popular atualmente?
Syntactically, it's a little backwards. As far as i know, in both portuguese and spanish the descriptive element (mais popular) almost always comes after what is being described (filme), so while your sentence has all the correct elements, the phrasing is backwards. It should say "qual è o filme mais popular hoje/atualmente?" instead of the other way around. The english equivalent of that grammar mistake would be like saying "what is the film most popular today?" instead of "most popular film". Its subtle. Hope that helps a little.