"Where is the animal?"
Translation:Var är djuret?
None really, but it's more idiomatic to say var då. If you just ask var, it may sound a bit abrupt and/or childish.
On the other hand we don't use var då in longer questions, like here, there's no way to add a då to this sentence. So basically it's added to avoid saying simply Var? as a one-word sentence.