This article goes over adding skills and has a link to the Larian video:
http://www.pcgamer.com/how-to-set-up-divinity-original-sin-2s-mod-tools/Here is a tl;dr:
1. Create an add-on type mod
2. Load "The Hold"
3. Search the root templates for the Skillbook you want
4. Drag and drop to location
Add to chest:
1. Search root templates for a chest, box etc
2. Right click and pick "create new from selected"
3. Change Display Name and file name to a new name
4. Go to "Items" section and add Skill Book(s) and save.
5. Drag and drop to desired location
oh and publish locally