One of the correct answers was misspelled: "What clothes is your bother wearing" - it should be bRother instead
Is another translation here, "What kind of clothes..." or "What sort of clothes...?" Or am I misunderstanding the jak-- words?
The question "Jakie ubrania..." is very general, and depending on the context, the answer could be close to anything: their colour, fabric used, region or tradition they resemble, quality, chicness, particular dress code, style, etc... Asking about kind or sort of clothes would be more "Jakiego typu ubrania...", "Jakiego rodzaju ubrania..." - so translating the sentence to "What kind of clothes..." would not be a literal translation.
I do not know how the course creators are strict about these translations. From some other courses I would expect this answer not to be accepted. If it were, surely with a hint that this is not the best answer expected.
It is perfectly good English to also say "what sort of clothes does your brother wear" (instead of 'what kind of clothes'; unfortunately, duolingo is not English and maybe International English does not use this expression. To pech!