Larian Studios Forums Divinity: Original Sin 2 - The Modding Dungeon Divinity - Original Sin 2 - Modding Guides Tutorial - Making an NPC sit.

You can use a "stool" ..try "GameMaster_Stool_01"
When you place the stool, turn off snap to floor and translate it so the top of the stool is just at ground level and follow the tutorial above.

The NPC will then sit at ground level.

His legs will be below ground I am afraid so you may have to decorate around them. (rugs or something ?)

alternatively ... stick a stool "inside" a rock. The NPC will then sit on a rock. That would look good around a camp fire.