"What is in the park?"
Translation:Що є в парку?
No, it is not imperative. In this case, however, the use of the word є indicates that we want to know what is present, what exists in the park. It emphasizes the being-ness of things.
Without Є it could be a question in response to a conversation about something that's happening in the park. If two people are discussing a festival, someone who overhears them might ask Що у парку?
But Що є у парку? unequivocally indicates that the asker wants to know what exists or is present there and the answer could easily be "trees, playgrounds, people with dogs, etc."