To save everyone else the headache, I’ve found each piece needed for this quest. The items are small and sometimes partially hidden so you’ll have to look carefully. Here are the coordinates for each:
Kith Kark’s Saber: 158, -471
Mandalorian Armor: -304, -756
King Ommin’s Exoskeleton: -168, 461
Queen Talia’s Necklace: 328, -1077 (entrance); necklace on shelf at 328, -1124
Tome of Freedon Nadd: 662, 390 (in the crypts on a shelf)
It’s worth doing this quest as it gives a big Onderon reputation boost.