You didn't say what software you will be using.
Probably depends on what software you will be using, check their documents and/or help files.
Radio Shack historically has not released protocol for its scanners since they often sold licenses to for profit software vendors who write such programs. The PRO-2051 was never particularly popular and is supported only by Scancat as far as I know. The Scancat site indicates the radio had two firmware versions that need different program timing. Baud rate is 9600 bps according to info on the Scancat site.
If Scancat has a free demo version you can use a serial port monitor to learn the commands by running the demo. The radio also has a clone mode that may provide another way to reverse engineer the protocol using a serial port monitor. Maybe all this would be more entertainment than you bargained for but I don't expect you will find the protocol spelled out in a file on the web.
I was afraid that was the case, as a thorough Internet search turn up nothing.
I'll see what the Scancat demo looks like, if it can be run on Wine.
Thanx for the suggestions.