"Where are you working? In a market?"
Translation:Càit a bheil thu ag obair? Ann am margadh?
Just as in English, In a market could equally be a question or a statement. Unfortunately the speakers on this course don't always seem to get the appropriate intonation so without hearing it I cannot tell if it was a question. If it was in written form just copy the punctuation given.
As far as real spoken Gaelic is concerned, you will often hear this.
As far as real written Gaelic is concerned, it is very rare in my experience. Mark does not use the word once. AFB says it is a 'colloquial short form' and Dwelly says 'for càite'.
The few comments there are on Duolingo are all at least 6 months old and there is a suggestion it was a form that someone put in that is being edited out of the course.
I would say that you definitely do need to be aware of it as a common word in spoken Gaelic, but unless someone sees it again in the course we can assume that it has been edited out as not being used in writing.