If you have tutorials enabled, the first time you pick up a weapon susceptible to breaking, the game will give you a pop up tutorial. Such weapons will have a marker to indicate they are breakable as well. Equip the weapon and during battle just fail on all your random rolls during an attack. I picked up a Torch early in the “for the king” campaign and equipped it on a minstrel (not great with physical weapons) and their success odds were fairly low with it and it broke on the second attack.