Posted September 21, 2020

1) install the latest ScummVM: www.scummvm.org/downloads (the current bundled version does not support subtitles, GOG should update it), run it and add the game in GK2 install directory
2) download the subtitles patch from www.sierrahelp.com/Files/Patches/GabrielKnight/GK2Subtitles.zip and unpack zip and also exe file in it with freeware 7-Zip: www.7-zip.org
3) copy all files from SUBPATCH folder to PATCHES folder in GK2 install directory and overwrite the current files
4) run GK2 in ScummVM - subtitles should be in the game and also movies

It seems it only works with the latest SCUMMVM version and doesn't work with the current built in version of GOG Galaxy. But if you want to use GOG Galaxy you can do as follow :
- Install the patch as explained above
- Install the latest SCUMMVM on your computer
- In Galaxy, in the GK 2 page, clic on the option then "Configure"
- In "features" select "Custom executables / arguments"
- Duplicate "File 1" which should be the scummvm.exe inside the GK2 installation folder. Then in the new File created (the duplicate) change the path for scummvm to the one you just install instead of the one built in.
- Tick the "default executable" for this file.
- Start the game from Galaxy. It will launch the latest scummvm from your computer. From here add GK2 to the game list. Then exit.
The next time you will start GK2 from Galaxy it will launch the game directly from the latest SCUMMVM and the subtitles will work.
Hope this helps
EDIT : This won't be needed once GOG Galaxy will update to SCUMMVM 2.1.xx