As Hood said, pick a free input pin number (10 - 13, or 15) and connect to that. Go to Ports and Pins / Inputs and assign your selected pin to Index. As with a lot of CNC4PC stuff, you may have to show it active low, or active high to get it to work.
I cannot understand where you are getting the 5 volt supply from, however. Do you have a break out board, or not. If you have a breakout board, you will find a 5 volt supply on that - but then if you have a BOB you will be inputing the signal through that, surely.
If you do not have a BOB, you will have to make up a small 5 volt supply. A small plug/transformer will do - like the phone chargers or similar, with a 5 volt voltage regulator. Connect the 0v side to the common return of your parrallel port (pins 18 to 25) and the 5 volt to the CNC4PNC board. There is no 5 volt supply on the printer port cable. I assume the 0v side of the CNC4PC card is already shown as connected to the 0v side of the printer port.