The item with the annular grooves is a ferrule which fits over the end of the housing which contains the cable. The ferrule fits into the socket of the derailleur's barrel adjuster which consists of the grey piece with longitudinal grooves, which you turn with your finger and the silver piece which moves in and out to change the effective length of the housing, often incorrectly referred to as "adjusting the tension". There may be other ferrules and sockets at the ends of various runs of housing as well as at the shifter. Any of these points may have become dislodged from the sudden shock of hitting the pothole, changing the effective length of the housing and upsetting the indexing adjustment.