How to measure voltage in a duplex (three-way) wired switch?
What you are looking for is called "Three way switches", although it will only be two switch locations. There are several wiring schemes that can be used, depending upon where the main power is derived from, switch box or light fixture. This link explains 8 different scenarios. 

One box will have the feed voltage, 120 volts ac. It can be in either of the switch boxes or the light fixture box. Any readings across the switch terminals would depend on the switch settings and that would require a light bulb installed that would complete the circuit.