Usually on the side of the door for a Bosch. If not, maybe on the front of the machine at the bottom, the bit you can only see with the door fully open - ie horizontal.
Mine is on the top of the door on the steel as you look from above, and can be seen easily if you open the door. It took me ages to work it out as Bosch told me it was on a separate steel plate. It is actually incorporated into the body of the steel.