Schematic Question with electronic button
The device in the diagram is an opto-interruptor. When the coin drops, it breaks the light beam from the LED (the upper "arrow with a line through it") to the photo-transistor (the lower "arrow with a line through it"). 

Some other board in the system will be providing power to both pin 1 and pin 2. When current through the photo-transistor stops, it will likely be interpreted as a coin drop.

If you break the wire from connector pin 2 and the photo-transistor, and put a momentary normally-closed switch (be careful about just taking any switch from your junk drawer: normally-open switches are probably more common than normally-closed) in series you will likely be able to fake a coin drop. Breaking any of the wires and inserting an NC switch would actually be likely to work (either by cutting off power to the LED) or breaking the PT circuit like the PT would do in the event of a coin drop.