Have your characters you want to train here.
Making them encumbered makes them train strength and making them sneak trains stealth.

Find this Copper node and shift + right click it.
Now the character should try to run toward it, but instead of reaching it they turn around to run back a little then run toward it again over and over non stop.
This happens because the pathfinding is broken for that spesific direction toward that copper node.
you can move them to it manually and they will run over as if the pathfinding is working fine.

It only happens if they have it as work priority that the pathfinding breaks.

Edit: The pictures don't seem to work and in too lazy to update them, but the copper node with glitched pathfinding is behind the shinobi thieves.