Right answer:

Dónde

Julio: ¿Dónde está la recepción?

This sentence translates into:

Julio: ¿Where is the reception?

So the word dónde translates into where. In this way, Julio wants to know where it is the reception. Perhaps he is arriving at a hotel and asks someone where this place is. So this is an assumption because there is no any context in this problem.