This Datacron unlocks the codex entry - Galactic History 60: The Destruction of Ossus
This datacron holds unheard of power and knowledge collected by an ancient race. You access its power and discover writings which are clearly only one small piece of a massive galactic history:
The Brotherhood of the Sith had annihilated the Cron Cluster in a supernova, sending a massive shockwave towards the planet Ossus. Home to the Jedi for countless generations, Ossus safeguarded vast libraries and storehouses of artifacts.
As the Jedi scrambled to save their treasures from the coming cataclysm, the Sith Brotherhood leaders Exar Kun and Ulic Qel-Droma arrived to raid the planet. Exar Kun managed to claim a number of notable Jedi artifacts. Meanwhile, Ulic fought against the Republic and Jedi forces only to be challenged by his own brother, Cay.
The two brothers fought until Ulic finally struck Cay down. The shock of his brother's death left Ulic stunned with horror. The Jedi Nomi, who had once loved Ulic, was overcome with grief and used her tremendous powers to somehow sever Ulic's connection to the Force. Left powerless, Ulic wept at what he had become.
This Datacron is located in southern Quesh and is one of the easier ones to get to here. To start towards this Datacron head over to where I am in (Screenshots 1 & 2). From here you will want to follow the white rock ledge west until you hit the wall and then south down and around the tree. Now it gets a little bit tricky around where I am in (Screenshot 3). Here you will have a giant rock in your way. What you need to do is skirt around the right side of this rock. If you fall onto the little metal ledge stub-thingy that's ok you can get back up to land from there.
Once you make it by the rock continue south following the white stone and using that as your guide. After you go around a corner and come out to a quarry looking area you will be able to see the Datacron in the very short distance (Screenshot 4).