"Where is the animal?"
Translation:Var är djuret?
Var is used for position and vart for direction. So if you want to ask where something is you would use "var", but if you want to ask where something is moving, you would use "vart".
Var är du? - Where are you?
Vart går du? - Where are you going?
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.