Two ways to tell... one, the factory installs a steel tag at the 1 o'clock position advising of the requirement for a Friction Modifier additive if the Tracloc is present. Or, jack up the rear so both tires are off the ground and spin one tire forward with your hand. If the other tire moves in the same direction a Tracloc is present. If the other tire moves in the opposite direction, there is either no Tracloc present or if present the Tracloc's clutch pack is worn out. There will also be a sticker on the inside of the glove compartment door warning of a limited slip's presence if it's there.
99% of the gear lubes you'll find on the store shelves will have the required Friction Modifier additive already there. If it's there, the back label will say something like "Compatible with Limited Slip Differentials" or words to that effect. If it's there, don't add any more.