There are 7 unique codex entries in the Lore section on Tython. 2 are accessible to all players regardless of class or faction and 5 are class specific.
Holocron | Coordinates: -331, -564 | Location: Tython: Jedi Temple
Holocron is from speaking with Master Yuon Par during "The Path of a Jedi" mission as a Jedi Consular or Master Bela Kiwiiks during "Enemy Force" mission as a Jedi Knight. Holocron is unobtainable for Smugglers and Trooper characters.
Codex type: Locations | Faction: Republic | Class: All
Associated Achievement: Loremaster of Tython
Jedi Weapons | Coordinates: 13, 1573 | Location: Tython: The Ancient Forge
Jedi Weapons is from interacting with The Forge during "The Forge" mission as a Jedi Consular or "Weapon of the Jedi" mission as a Jedi Knight. Jedi Weapons is unobtainable for Smugglers and Trooper characters.
Codex type: Locations | Faction: Republic | Class: All
Associated Achievement: Loremaster of Tython
Malachor Three (Consular) is obtained from interacting with the Jedi Council Chambers during "A Return Home" mission.
Codex type: Lore | Faction: Republic | Class: Jedi Consular
Associated Achievement: None
Rebuilding the Jedi Order is obtained from interacting with a Clickable Chair.
Codex type: Lore | Faction: Republic | Class: All
Associated Achievement: Loremaster of Tython
Rediscovering Tython is obtained from interacting with a Clickable Plaque.
Codex type: Lore | Faction: Republic | Class: All
Associated Achievement: Loremaster of Tython
The Emperor's Plan (Knight) is obtained from interacting with the Jedi Council Chambers during "An Unthinkable Alliance" mission.
Codex type: Lore | Faction: Republic | Class: Jedi Knight
Associated Achievement: None
The Principles of Rajivari (Consular) is obtained from speaking with Master Yuon Par during "The Footsteps of the Fallen" mission.
Codex type: Lore | Faction: Republic | Class: Jedi Consular
Associated Achievement: Loremaster of Tython