The Schnitzel changes location on a timer. It appears hourly. You will see a white message, The Schnitzel is looking for a new hiding place. If you are lucky and have the special event item, the talking sausages, they will tell you the location. You can also check locations it has spawned before, because although the city may change, the location in that city stays constant, so you can mark the cauldrons the Schnitzel appears in on your map.
If the Schnitzel is killed, it will respawn at the next due time.