Although there is no reference to the size of that rubber bumper, I can only see one place that looks possible to me.
My attached photo shows the flat metal strap that limits how far the door opens. I suspect that the rubber bumper mounts on that strap on the inside of the door frame and when the door is opened to its limit, it provides a cushion when that flat strap is at the limit.
If that is in fact what it is for, I probably need two of them for my car as well.
Scott