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
Alderaan – 5 Datacrons
Green: Endurance +3
Location: 2721, 2494
This Datacron is hidden inside a cave wall that you must destroy. Find the entrance to the cave at 2374, 2450. Follow the path straight in. Eventually you will a blast pack on the wall. This pack can be used to blow away the rocks hiding your Datacron.
Red: Strength +4
Location: 2191, -2018
This Datacron is located on a small ledge on the face of the dam. From the backside of the dam work your way to the following location: 2240, -2026. From there jump down but use the obstacles along the way to break your fall. From here there is a “Magnetic Stabilizer” that hovers above the platform with your Datacron. If you click it (you should be able to reach it from the ledge you are on)it will pull you over to the platform.
White: Aim +4
Location: 1105, 80
This Datacron is located on the island that is only accessible via the trolley. The trolley is very slow, so you have to be patient. The entrance to the trolley can be found at 1090, -7.
Purple: Willpower +3
Location: -2507, -425
Start inside Castle Panteer at coordinates -2490, -368 there is a crack near a door that you can slip through. Follow the path until you’re on the 2nd floor. From there you should see the Datacron. Follow the hallway / landing to the right and all the way around to collect it.
Yellow: Presence +3
Location: -81, -268
In Glarus Valley there is a large bridge that is held up by a giant rock. This Datacron is located about halfway up the rock. Head to coordinates -412, -209 and you will find a Thranta nest. Click on the Thranta and you will receive a codex entry and also a ride up the hill to this Datacron. Easy.