They aren't asking which question is more common in English. This is the correct translation of "whose is the coat?" Remember that the way that english speakers say things will be different than the way italian speakers word things.
"Whose is the coat?" This sentence is awkward as it tries to be grammatically correct. There are many ways to ask this question. More appropriately one can say: "Whose coat, is it?" Or simply, "Whose coat?" if the speaker is pointing at it or holding it up.