A tip for Duo: when "é" comes by itself refering, translate it as "it is". Your sentence would probably be accepted if the original sentence were "De quem é ESTA camisa?"

I agree that your version is OK.

I'm sure you personally are way beyond the need for any answer but other people who are new read these discussions so I will answer anyway. :)

"Whose shirt is this" introduces another word into the sentence which has a Portuguese equivalent (esta).

Repeating Paulenrique's comment above:

A tip for Duo: when "é" comes by itself refering, translate it as "it is". Your sentence would probably be accepted if the original sentence were "De quem é ESTA camisa?"

So, perhaps, "Whose shirt is it?" would be best for English speakers to accept.

"Who's" means who is (or who has) so unless, "shirt" is a proper name or perhaps job position, that won't work.

"Whose" is the possessive of who.

http://blog.oxforddictionaries.com/2016/02/whose-vs-whos/

But I agree, "Whose shirt is it?" flows better; though the other [DL translation] works just as well and would get the business of understanding done.

Who = quem (quien, quienes). Whose = de quem

I think francophone will be tempted to see 'de' a direct translation of DE QUI ...but it shouldn't be understood that way.

"who is this shirt from" would be OK if it means the shirt was delivered, as a present for example.

Whose = De quem (its translation takes 2 words in Portuguese)

This sounds awkward in English.

Not wrong, but you will hear "De quem é/são...?" all the time.