How do I connect my printer encoder to arduino?

Hello.

First of all, I am an amateur.

I have a multimeter, but how do i find it?

First you need to know what type of interface it has. Is there anything printed on the board near the pads that you indicate ?

It might be simply an LED and two photo-transistors - 6 pads suggest this, the two on one side for the LED,
the 4 on the other are the photo-transistors. Try looking at the voltage on any of the photo-transistor pads
as the carriage is moved very very slowly (these printer optical encoders are very high res).

What is PED? Also called pin?