Translation:We have a job offer in the paper.
Well, according to Pons it can also mean "vacant position" : http://en.pons.eu/translate?q=Stellenangebotl=deenin=ac_delf=de
So you probably shouldn't report it :-P In fact, in this sentence "vacant position" fits much better than "job offer", at least the way these terms are used in American English: Usually a job offer is what you get after you apply for the vacant position and pass the interview. The job offer includes the company's proposition for your benefits and compensation; and you then get to accept or reject the offer.
In English the assumption is pretty clear: If an offer is in the paper you're misunderstood the posting or the poster in insane.
A job offer is presented to a candidate that the company wishes to employ. It would never be publicly posted. Similarly an employment advertisement might be published IN the newspaper, but if the job is AT the newspaper then the advert, or offer, will be either AT of WITH the newspaper.
That's actually pretty exact.
I don't know if it's considered colloquial or not, but I think that most people actually say "Job Notice," for what Duolingo is looking for here. Unfortunately, it will not count as correct. "Vacancy," is really used more for letting people know that some position in the office is vacant (but not necessarily available--the company may not actually be trying to fill the vacancies with new hires). To say you have a vacancy in the paper is unclear because it may imply that a job is available at the newspaper itself for, for example, an editor or a journalist, or it may mean that there's something else missing about the newspaper, like an open spot for an ad. No one would actually say this, so it's difficult to really translate what it could mean.