Where is the transmission fill plug on a sportster?

Look at the low side of the bike (battery side). The large cover on the side of the engine that covers the clutch assembly is the primary cover. It has a smaller circular piece that is held in by two Allen head bolts above the area where the clutch pedal attaches. When this is removed you can check the primary chain tension and put in the clutch lube. If someone has put a chrome cover piece over the primary then you will have to remove this in order to see the inspection cover that I am referring to.