On start-up “3DCoat for Linux” automatically enables tablets which it is able to recognize. 
Otherwise the tablet should be enabled manually by defining the environment variable “COAT_PEN” equals the name of the input stylus device. 
Wacom
For example:
export COAT_PEN=”Wacom Intuos3 4×6 Pen stylus” 
Since “3DCoat 4.9.70 for Linux” it outputs into the Terminal the list of your input devices.
Please see the attached screenshot as an example.
You have to send a screenshot with the name of your input stylus device (similar screenshot as the attached) to me (support.linux@3dcoat.com). 
Then your input device name will be added into “3DCoat” to automatically enable it in the future builds.

You have to add the tablet name a first time before it revealed more input device names. 
One of the new ones revealed will be the correct one. As example  “XP-Pen Pen Pen (0)”.
Sometimes adding the mouse device made the scroll wheel stop working inside 3DCoat – however leaving the mouse variable empty it work.
X-Pen
Start 3DCoat in terminal and see what Input devices it will give you. Than set environment variable according to that, before starting 3dcoat next time.
As example:

So next time before starting 3DCoat from terminal, you will setup env variable by executing
export COAT_PEN=”XP-Pen Pen (0)”
than start 3DCoat.
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