There's no indication in the Korean that the answer should include "for us", so shouldn't the answer just be "Who wrote the weather forecast?"
When you add 주다 to a verb it implies that it's done for someone, so yes it should be "for us" or "for me" or something.
Am struggling to figure out in what context this example sentence should be used.
When we end up working in a Korean news production company. Isn't that the goal of every Korean student?
I think Duolingo updated it and "Who wrote the weather forecast?" just got accepted as a correct answer, so you weren't entirely wrong :)
The "for us" part is implied in English, so although the direct translation includes "for us" it doesn't need to be there to make sense in English. If you're going for a more natural translation, remove the for us, if you're going for a more literal translation, include it.
Shawn's question is really good, especially with the thoughtful responses given. I'm disappointed that his question has a negative rating. What on earth are people rating it on?