Plenty of options to choose from.
Grommet in the stator cover that seals up the wires.
Stator cover gasket.
Mid gear cover gasket.
Loose bolt on the mid gear cover. As KJ noted, there is one bolt on the mid gear with a copper washer. If that bolt is loose, you can leak oil.
Seal on the front of the differential. Diff oil travels up the swingarm and comes out of the hole in the bottom of the rubber swingarm boot.
Similar to above but instead of diff oil, engine oil leaking past the output shaft seal. It can make its way out the rubber swingarm boot.
If you have never opened up the stator or mid gear covers my first guess would be the shift shaft seal. It can be replaced by removing the shift lever and the linkage. Pull the snap ring retaining the shift lever and totally remove the bolt securing the linkage to the shift shaft and remove as a unit. Put a small screw in the seal and pull it out. Grease the lips of the new seal and carefully tap in place. Take note that the shift shaft is marked so you can properly index the linkage upon reassembly.
Best bet is clean things up, warm the bike up and observe so you can determine the actual location.