Shock absorber mounting bolt.......
Dont know the size but they are about £1.50 each from most specailists. Check all the others are tight and that the locking tabs are holding them tight. I wouldnt drive over too many speed bumps intil you fit a new one
If they sheer off this area is a main structural area and a difficult place to repair properly.
If it is sheered off then you will have to remove the Damper (the spring absorbs the shocks the damper smothes out the occillation) If you are lucky there will be enough of the bolt showing to get a wrench on to it. If its sheared level with the bulkhead then you will have to try an extractor.