You will be able to see Datacrons from quite a distance as they emit a large glow around them and shoot a beam of light into the sky. If you are very close to a Datacron you will also be able to hear the sound from them.
Datacron Locations By Planet
Tython (Jedi Knight / Jedi Consular Origin World) – 3 Datacrons
Blue Matrix Shard (Unlocks Galactic History Entry #11)
Location: -93, 919
If you walk south of the Forge Remnants there is a path that leads to this Datacron. The beginning of the path can be found at -195, 812. The Datacron is at the top of the raised area and is guarded by an elite Flesh Raider.
Green: Endurance +2 (Unlocks Galactic History Entry #9)
Location: -33, -101
This Datacron is located in a cave due east of the Forward Camp Speeder. The entrance to the cave is located is at -28, 22. It’s pretty easy to get to, you will have to kill a few Flesh Raiders along the way.
Purple: Willpower +2 (Unlocks Galactic History Entry #10)
Location: -642, -70
Head to the Ruins of Kaleth, take the stairs to the second level of the ruins. Go into the building on the right. Inside you will see a pillar on the left coming down from the roof into the room. Walk up the pillar to reach the third level of the ruins. Turn right and walk across the fallen pillar to the forested / hill area. Your Datacron will be in front of you on the right hand side.