From what I've seen in the codex, there are five datacrons in Quesh. I have four of them. Everywhere I've looked only has 3 locations. The fourth one I found in an area I clearly can't get to anymore because I can't seem to find it to verify the location. It involved jumping up on a bulldozer, then to some pipes, then to some crates, over to a big pipe, back to crates, over to some platforms, and down into a bucket I believe. It was in an indoor area with droids and I think it's one of the areas near Imperial Outpost.
Anyways, I have some theories on the 5th one but I can't seem to find it anywhere.
One of the places which I'm most confident it has to be in is a blocked off passage at 116, 1075 (northeast of Imperial Forward Command Center - at the big building with the elevator that goes to the roof and the droids in front of narrow passageways looking out). An invisible wall prevents me from getting in through the front side and I've no clue how to get to the back side - and I tried approaching it from above, but I couldn't get to the right spot to jump down.
Another spot is at the Imperial Garrison. I got through the fence and explored that area but could find anything. I was able to get up on the pipes but that ended up being a dead end.
Also there is a spot in the southeast corner of the map where a small passageway leads you to an open area which contains a lore object. I could not get the lore object to grant me any lore as nothing happened when I clicked it, nor did I see any datacrons.
There were also two other areas that I was able to get to through what I thought were obvious datacron path starters and both involved jumping down - but both jumped me down to a blocked off area where I could not get back out. (One area was near Conk's Infinite Loop, the other was the northern-most center area.)
Does anyone have any clue where this 5th one is or any pointers on how to go about looking for it?