Hi,
It is one diode for generating the light ( two leg easy to figure out just
use a battery and a 1k resistor if Your drop will be between 1.8 and 2.5
volts that is Your correct polarity )
The other side is a photo transistor ( three legs ) With a diode checking
multimeter You can figure out which is the base.
After it is easy just measure the forward drop on BE and BC diode . The
higher reading going to be the emitter.
Hope it helps,
PeterS