Good Old Games doesn't usually re-write Windows games for OS X; it just wraps them in a .app with Wineskin and then puts that file alongside the necessary files for running it on OS X, and packages the whole thing in another .app file.
So to get to the saved-game files on GOG's OS X version of Wizardry 8, you have to:
- Show the package contents by right-clicking on Wizardry 8.app wherever it is on your hard drive, and choosing Show Package Contents
- Navigate the file structure (/Contents/Resources/Game) to ANOTHER Wizardry 8.app.
- Show the package contents of this app-within-an-app.
- Inside the nested app you'll find the original Windows file structure: /drive_c/Program Files/Wizardry 8/Saves.
This save folder has your good old .SAV and .CHAR files which can be moved to the same location on another Mac computer.
It looks like I could even move .SAV and .CHAR between Windows and OS X copies of the game, since GOG doesn't modify the Wiz8.exe that actually runs them. This makes sense, given the Wizardry franchise's history of porting old campaigns into the next game in the saga--and the Wizardry community's tenderly cherished vision of a new Wiz game being released in some glorious future.