"You do not know if the cook has the fish."
Translation:Tu non sai se il cuoco ha il pesce.
According to the "btw you are wrong" message from DL, sappia is the imperative form. Furthermore, when hovering over "know" in the sentence, a list of only imperative forms drops down. Since this isn't an imperative exercise I can't help but conclude that this deliberate misguidance is sabotage on some developer's part.
I don't believe it is sabotage, but a - rather unsatisfying - compromise solution. Hints often seem to give only dictionary entries, regardless of context. If there are many possible interpretations, only a subset is presented. And that subset, however it is selected, is unfortunately often not matching the context.