little help?
there is no real easy way unless you have a data sheet, run a couple wires from the arduino's 5v power and ground
on the 5v wire add a 220-470 ohm resistor, connect the ground wire to a pin on the display, poke the other pins to see if something lights up
if not, well its kind of a process of elimination, if its attached to a pcb you may get lucky and notice that a pin or pins are connected to the ground plane
A real image of the device you have might make it easier for us to guide you