"Whose jacket is it?"
Translation:Wessen Jacke ist es?
Same here. "gehören" = "to belong" came totally out of left field. Luckily "Wessen Jacke ist es" was accepted, but when I looked at the other correct solution according to Duo I was mystified. I could not understand what "to hear" had to do with jackets! At least now I have learned a new word, but it was a weird process! (I never use word blocks, so I cannot say whether "Wessen" was in there.)
It accepted "Wem gehört die Jacke" (to whom does the jacket belong) also.
The sentence didn't specify a particular jacket so I didn't use "diese", although in context, as opposed to an isolated sentence, it would be clear that they were talking about a specific jacket.
I found an online source that says that although the "Wessen" construction (whose) is correct, the "Wem" (to whom) construction is more commonly used.
It's hard to explain properly, but ‘es’ isn't quite referring to ‘Jacke’ just yet. Think of how you can say ‘who is it?’, for example on the phone, when whoever's calling is definitely not going to be an ‘it’. Better yet, think of how you would express this as a statement: ‘that is Jenny's coat’ = ‘das/es ist Jennys Jacke’. The ‘that’ at the beginning is referring to a general thing that you haven't identified as a ‘Jacke’ yet, which is why you would use a neuter pronoun in German too. In the question the order changes because of grammar, but the subject (‘es’) is still fundamentally the same and still doesn't have a noun as a referent to take the gender from.
Usually there are many possible translations for a sentence. "Wessen Jacke ist es?" is definitely one of them. But maybe not the one that could be built using the words you were given. The "main solution" (see top of the page) uses even very different words: "Wem gehört die Jacke?".
So maybe you gave a wrong answer that started with "wessen"? Then Duolingo would have suggested the correct answer closest to yours, which might have been "Wessen Jacke ist es?", even though you couldn't have built this sentence using the word blocks.
Your mistake was using "dieser". "Jacke" is feminine, so it should be "diese Jacke".
Since Duo tries to find an acceptable sentence as close as possible to your answer, and works from left to right, a possible completion of the sentence was suggesting "Mantel", which is masculine and means "coat".
The verb should be in second position. That does not mean it is the second word, but the second grammatical element of the sentence. The first element is "whose jacket", these words belong together.
Besides: the "verb second"-rule holds for affirmative sentences, not for questions and orders, so it doesn't apply here, because it is a question. And questions have different rules. Often the verb comes first in questions, but in questions headed by a question word, it goes second again. This is what we have here, because "wessen" is a question word.
"wessen" is the translation of "whose". It is not an adjective that qualifies "Jacke". So it doesn't matter what gender "Jacke" is.
Btw., the relative pronoun "der" indeed has similar endings. Its genitive is "dessen" for masculine and neuter persons. For feminines it would be "deren". But of course "dessen" and "deren" does not follow the gender of the thing possessed, bit of the owner. And the question word is not gendered at all. It's always "wer" resp. "wessen" (because you are asking. You son't know what gender the person you ask is).