The editor for D:OS 2 can open saves, after which it is possible to select a character or item and use the 'export to .obj' option (or 'export scene'). There isn't a way to go directly to a 3D print friendly format, though, as far as I know. The D:OS editor can not open saves, but you can place or recreate characters/creatures/etc.
The exported obj will not contain the normal maps that are used to add some texture to the models.
In the Steam library, top left dropdown, select the option to show Tools, optionally unselect Games, then check the Tools section of the list for 'The Divinity Engine 2' and 'The Divinity Engine Enhanced Edition' (searching for 'divinity' first should shorten the list).
With the GOG versions, the editor is a separate download in the games' extras, in the library page for each game.
I don't know if anyone in Larian's Discord
has done any 3D printing, but you should find some information there on working with models, in addition to the mod forums here.