There should be an individual track gain knob or slider. Caveat: I don't have any experience at Sound Forge but I do with half dozen other true DAWs.

You cannot open 2 tracks at once so there is no gain control for a track that isn't there. I tried using Adobe Audition which displays several tracks at once, but in order to use their pitch control you have to use Edit Mode and once again, only one track is displayed. Sound Forge has a much better Pitch Bend Tool, so I'd rather use that app.

Melodyne

Once you have made your destructive edit on the track (in Edit View), you just duplicate the pitch adjustment on the second track in the same manner. This will then translate to the multitrack session view. Now you will be able to adjust your individual volumes. Better yet, mix to taste first and THEN take your final mixdown and apply the pitch adjustment in edit view.

I guess I'm not being clear. I am not trying to make any volume adjustments and I do not want to apply my pitch changes to a 2nd track.
I want to listen to both the vocal track and the accompanying music track at the same time. Since I don't have a pitch perfect ear, I cannot tell if the vocal is off key at any point without hearing the singing and the music at the same time. As I listen to both tracks I want make all my pitch adjustments to the vocal track only.

hueseph wrote: Melodyne

I don't think you can do this in Sound Forge hence the link to Celemony's Melodyne.

Melodyne seems to do exactly what I want. And for only $700. Sheesh.

A cheaper option would be to transfer the backing track to a CD.
Then hit play on both the CD player and Soundforge.

Perfect? Hardly. Annoying? Yes.
But it won't cost you $700.

Another solution (for the future) would be to record the vocal, note the points where you have pitch issues, and have the vocalist retake those in tune. Then comp the in tune portions together.