There's nothing wrong with this English sentence (where can we get the best dumplings), but it doesn't give any hint as to what's expected in Chinese. "Which place has the best dumplings" would at least be a little closer.
Translation is indirect. It should be accepted, but it shouldn't be the shown correct answer. The Chinese sentence is more like, "Where has the best dumpling," completely neglecting the "we get" from the English sentence.
Yet another example of "memorise what Duo wants" instead of "apply the Chinese you actually learned".
The translation would be fine if it was a subtitle for a film, but it's terrible as an exercise for learners.