"هٰذِهِ صَحيفة اَلْمُهَنْدِس."
Translation:This is the engineer's newspaper.
Away from Duolingo's picky lines for correct answers (because contributors don't add many correct solutions), your sentence would be more like: هذه الصحيفة للمهندس (háThihi ac-caHeefah lil-muhandis). Literally: this newspaper is for the engineer.
Meaning-wise, your sentence and the sentence done by Duolingo both deliver the same meaning. However, grammar-wise and structure-wise, they are both different. To my experience with Duolingo, they would mostly emphasize the structure rather than the meaning.
To further analyze the sentences, here is a comparison:
- This newspaper is… : هذه الصحيفة…
- This is a newspaper: هذه صحيفة
The structure that Duolingo used here is the second, but with a twist, by adding the genitive (engineer's). In Arabic, genitive is done by adding words together (with the definite article, if it exists, added to the second term in the compound). Thus, the engineer's newspaper becomes صحيفة المهندس.
As I've translated your sentence, you notice maybe that there is no genitive involved: هذه الصحيفة للمهندس (this newspaper is for the engineer/the engineer's). I'm speaking about the genitive in the Arabic that is. Here, we state it as للمهندس (for the engineer). In Arabic this is somewhat a prepositional case (approximating the terminology here). Also, this sentence uses the first structure in the two examples above. The main difference between these two structures is what is the subject (i.e. what is before "is" in English) and what is the predicate (i.e. what is after "is" in English). Changing the order or what is a subject and a predicate in one language would eventually change them as well in the other language when translating as well.
Hope this helps.