I haven;t looked under one of those in a while, but the FSM shows the fill plug to be on the cover on the rear side of the assembly. The only reference to filling the assembly in the shop manual with any meaningful information states this: Remove the filler plug, fill the rear axle with 1.15L (2.43 pt) of rear axle lubricant, 3-5 mm (0.118-0.196 in) below the bottom of the filler hole and install the filler plug.
Tighten to 29 Nm (21 lb-ft).