Coordinates: X 778, Y 8
The Red Matrix Shard is located in southwestern Ord Mantell on the island of Mannet Point and is extremely easy to get to. Near the island of Mannet Point you will find a broken bridge, you will need to run across this bridge and jump off into the water below. Once you're in the water make a break for the island as a lot of this area is counted as an Exhaustion Zone, meaning you will take damage just for being out here. Once you make it across the water and to the island the path you need to take is fairly straight forward. The only other surprise is that cube is guarded by a level 6 elite. (ohh emm gee big deal)
Coordinates: X -977, Y 9
This Datacron is found on Ord Mantell at the coordinates -977, 9. That is on the northern beach of Mannett Point, for those not good with Coordinates. What you need to do in order to reach this Datacron is travel around the western end of the mountain (don't go inside, instead drop down off of the path and follow the beach around until you find the little divet on the map. This is where the Datacron is located. Honestly there is no reason for a super long explanation so here are a few pictures.
Coordinates: X -656, Y 44
This is by far the easiest Datacron to find on Ord Mantell since it is visible from a frequently traveled path. The Datacron is on Savrip Island which is in kinda southwestern Ord Mantell. This Datacron is just northeast of the Presence +2 one, you literally have to pass right by it in order to get to the Presence Datacron. For that reason I recommend grabbing both of these back-to-back before you head over to the Red Matrix Shard. Anyway, onto how to reach this Datacron. From the path that leads right by it (Screenshot 1) head across the river to Savrip Island.
Once on the island you will want to circle around back to the side that faces the ocean. From here you'll want to find a small little dirt slope that leads you onto the plateau opposite of where the Datacron is (Screenshot 1 & 2). Once here it's easy, make your way across the little rock bridge (Screenshot 3) and up onto the plateau. Once up here the Datacron is all yours!