This Datacron unlocks the codex entry - Galactic History 58: Ulic's Tale
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 was ready to strike. The fallen Jedi Ulic Qel-Droma, the Sith sorceress Aleema and Mandalore gathered their armies to attack Coruscant. But they underestimated Coruscant's Jedi defenders. The Brotherhood's forces were repelled, and Ulic was captured.
Ulic was taken to the Senate tower to stand trial. But the Jedi Master Vodo Siosk-Baas sensed that Ulic hadn't acted alone, that Siosk-Baas's old student, Exar Kun, was involved. During the trial, Exar Kun himself marched into the Senate tower with his Massassi warriors. He subdued the assembly with his Force abilities and humiliated the Supreme Chancellor.
Vodo Siosk-Baas then entered, challenging his former pupil. Exar Kun's unusual double-bladed lightsaber and dark powers prevailed, however, and Siosk-Baas was killed. Exar Kun and Ulic then left Coruscant and returned to Yavin Four to prepare for the next battle.
What you need to do to reach this Datacron is go to the area north of the Republic base on Quesh (Screenshot 1). Where I am standing on the map in the first screenshot you will find a pipe which you need to climb up ontop of to start the hunt for this Datacron (Screenshot 2). Once you're ontop of the pipe jump up onto the siding like how I am in (Screenshot 3). Now from here you will want to keep jumping in a southwesternly direction from stub to stub until you reach the large yellow pipe (Screenshot 4). In Screenshot 4 I am looking back at the area we just came from, so you don't get confused.
From the pipe you will want to make it to land and then follow the land west until you come to a large drop off area where you can actually see the Datacron (Screenshot 5). From here you will want to drop down and follow the northern end of the fence all the way around until you come to a break in the fence (Screenshot 6). At the break, go through and over to where you saw the Datacron before and bam, you're all done!