There are 3 Datacrons on Quesh available for both factions. Even if you won't find them lying in the middle of the road, all of them are quite easy to get to.
Datacron 1 - Republic and Empire
Codex Entry - Galactic History 60: The Destruction of Ossus
Coordinates: 558, 1422
The first Datacron is located in the Three Families Warcamp area. Go at 462, 1786 and you will see a wall. Climb the ledge that surrounds it and follow it around the wall until you get to the Datacron.
Datacron 2 - Republic and Empire
Codex Entry - Galactic History 58: Ulic's Trials
Coordinates: 425, -132
Go on the road north of the Republic Mining Camp and at 565, -180 you will find a pipe. Climb it, jump on the wall ledge in front of the pipe and follow it to the platform. Then go around the fence until you find a break in it and enter the fenced area. The Datacron is in the back hidden behind a few pipes.
Datacron 3 - Republic and Empire
Codex Entry - Galactic History 59: Aleema's Fate
Coordinates: 207, 773
The Endurance Datacron is located in Yunna Crosscut (there are entrances at -9,715 or 439,772). Before reaching the central area you will get to a door with a panel. Activate the panel while standing inside and the room will be filled with a poisonous gas that will constantly inflict damage. It's best you take a healing companion with you for this Datacron. Inside the room there are two pillars with panels. Run to the western pillar and activate that panel then to the eastern pillar to activate the second one. That will lower the force field that was blocking the entrance to the southern corridor and allow you to go there. You'll need to hurry throughout the process as the toxic gas will eventually kill you if you don't get to the southern corridor fast enough. The Datacron will be waiting for you at the end of the corridor.