Setup: Editor GOG
From Divinity Engine Wiki
1. Download from your GOG library
2. Move "Editor" folder to game's "Data" folder
Open the downloaded zip folder.
In order to use The Divinity Engine 2 please copy the "Editor" folder to "Divinity - Original Sin 2\Data" folder, for example "C:\GOG Games\Divinity - Original Sin 2\Data".
3. Launch The Divinity Engine 2
To launch The Divinity Engine 2 please use DivinityEngine2.exe
4. Initial setup
On starting up The Divinity Engine 2, it will ask for a game data path. Set this to your Divinity: Original Sin 2 'Data' folder.
It looks approximately like this for GOG: 'C:\GOG Games\Divinity - Original Sin 2\Data'.