That hole in the bell housing is where the clutch/flywheel/pressure plate is located. You may have to remove the metal protection plate if your car still has it, and the bolt could be sitting on it. Otherwise, next would be unbolt the starter motor and heat shield which will give you a lot of access to see if you dropped it in the bellhousing.
Just noticed now that you said your car is auto. I'm not that familar with the differences as I've only worked on manual 944's.
Take a look at this video starting around the 8min mark if you need some additional guidance on whats going on down there.
https://www.youtube.com/watch?v=KGIPx5WeDyM