At the top of the MooseEdit window there are 3 long text boxes, one for the 'Currently Loaded' save, one for the "PlayerProfile Folder' and the bottom one for the 'Game Data Folder'. Click on the folder icon to the right of the last one, and browse to the games's Data folder. The path displayed in that box should be something like:
D:/games/Divinity - Original Sin/Data/
IIRC the GOG installer points to c:\gog.com\... by default, or something like that.
