Since there is at this point in time very little info about making a discriminator tap on the radioshack pro-2055 scanner, I figured I would share my findings:
The pro-2055 is internally almost the same as the pro-97 scanner, so you can safely follow a guide for the pro-97. The pcb layout is just a little different, but it shouldn't be too hard to spot TP4.
I soldered a long wire to tp4 and a ground point, routed it through the speaker hole and exited the scanner through the hole in the middle of the back plate. Then added a 10K resistor in the wire. That's only because I didn't have a drill or a female jack at hand to make a fancy phone jack socket. See pictures below for the location of TP4 in a pro-2055, how I routed the wire, and soldered in the resistor. The pictures may be a bit blurry but that's because my digital camera is rather.. cheap.
Just make sure the wire is secure enough that when you move the wire on the outside of the scaner, it doesn't move on the inside. This will provent your contacts from breaking and causing shorts inside the scanner, which may damage it. Just use tape or a glue gun or something,... I just attached a mini-jack plug at the end of the wire so I can plug it right into the computer's line-in.
This worked like a charm for my pro-2055. I hope it does for yours too.
Please don't sue me if you break your scanner or poke yourself in the eye with your soldering iron. I don't have any money anyway.