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
Ord Mantell (Trooper / Smuggler Origin World) – 3 Datacrons
Red Matrix Shard (Unlocks Galactic History Entry #14)
Location: 778, 134
This Datacron is north of Mannett Point. It’s located on the beach on the very north side of the island. You simply have to run around the island on the beach to reach it. It’s guarded by a couple level 6 elite mobs and a level 7 named mob.
White: Aim +2 (Unlocks Galactic History Entry #12)
Location: -657, -575
This Datacron is located on peak in the center of Savrip Island. You should be able to see the Datacron from the beach when you fist arrive onto the island. Run up the beach and follow the fork to the left. A little ways down on the right hand side you will find an area where you can very easily start jumping up the rocks.
Yellow: Presence +2 (Unlocks Galactic History Entry #13)
Location: -975, 203
This Datacron is located just west of the Volcano on the beach. If you follow the beach from the Volcano Camp you will eventually run right into this Datacron. It’s very easy to get.