Ossus

The Ruined Wall contains 5 glowing runes, which indicate the order that the runes scattered around Ossus need to be activated in. Activating the runes can be tricky because there are no buffs or indicators that you have activated a rune. Activating a rune more than once will void the activation and you will have to restart. Some of the runes require some finesse with platforming, but it is more of an annoyance than anything because of how widely distributed the runes are.

The rune order is: Blue, Yellow, White, Orange, Green.

After activating all 5 runes in order you should return to the Ruined Wall, to ensure that you can progress to the next part of activating the holocron. If you have activated your runes in the correct order then a glowing yellow circle should appear in the upper portion of the wall above the runes. If the circle is not present it means your runes were not activated and you need to start over. If the circle is there then you can travel to the Jedi Library Ruins.

In the Jedi Library Ruins you will be able to enter the western phased area of the map, without the faction specific heroic mission, and this will place you in a special phased area specifically to collect the holocron. A part of the floor will be missing and this tunnel is used to access the upper section of the library where the Holocron of Ood Bnar is located. The tunnel is very dark, with seemingly randomly distributed mushrooms providing meager light. In reality the mushrooms mark the path that you must platform to reach the upper library terrace. Alternatively you can turn your shadows to low in the graphics setting and this will make the pathway much easier to see.

Once you have reached the upper terrace of the Jedi Library Ruins you will need to activate 2 Ancient Switches. Doing this will make the Holocron of Ood Bnar interactable, and additionally will put shields over the missing sections of flooring to make it easier to travel back and forth across the terrace. Activating the Holocron of Ood Bnar will cause the datacron to disappear and the final step is to travel back to the phased instance where the Ruined Wall was. A small pedestal in the water will hold the datacron which grants the bonus to endurance and the codex entry.