Looks like a later gearbox cover there....grease nipple and maybe that external nut hidden by the kicker. Also that lug is threaded (well it was originally) to take the clutch cable adjuster, this comes ready fitted to a new cable.....here it's clearly absent.
I'd suggest a trip to the local cycle store for a proper cotter to replace that shaft grinding nut and bolt, file the flat on the new cotter if required, and fit with the retaining nut to the front of the bike.
Swarfy.