Here is the full list of all 57 Star Wars Knights of the Old Republic II: The Sith Lords achievements.
Complete the game on the Light Side
Acquire all Light Side Powers
Side with the Queen on Onderon
Side with the Settlers at Khoonda
Change your mind about siding with the Settlers at Khoonda
Learn how to kill Jedi from HK-47
Deduce G0-T0's identity
Recruit Mira
Learn Moving Meditation
Reduce a companion's Influence to zero.
Recruit the Disciple
Learn Force Sight
Reach maximum Light Side points
Let the Sith destroy the Peragus Asteroids
Complete the game on the Dark Side
Defeat Sion
Have your character replace any of the Sith Lords on the main menu screen.
Reach Player Level 30
Claim Darth Nihilus' mask.
Defeat Nihilus
Acquire all Dark Side Powers.
Kill all the Jedi masters
Have 30 points in Demolitions.
Flee Korriban after fighting Sion
Get this by starting the "Trapped" Quest on Korriban.
Have 30 points in Treat Injury.
Have 30 points in Stealth
Install HK-47's unique module
Side with Vaklu on Onderon
Loot a body on Korriban
Win a Pazaak game with a full board
Have Persuasion over 30
Get the named Lightsaber crystal
Break Hanharr's spirit
Fill the Party Selection screen
Complete the Mandalorian Battle Circle
Teach the Handmaiden the ways of the Force.
Listen to HK-47's definition of love.
Repair the damaged droid on the Ebon Hawk
Contruct your first Lightsaber
Beat the champ on Nar Shadaa
Convince the "champ" to lose the game without playing.
Convince Vogga the Hutt to sell fuel to Telos.
Gain a Prestige class
Recruit Hanharr
Have 30 points in Repair.
Have 30 points in Computer Use.
Reach maximum Dark Side points
Recruit the Handmaiden
Complete the Handmaiden Battle Circle
Collect 10,000 credits
Get your first Light Side points
Destroy Peragus Astroids
Dance for Vogga
Kill all Sith troopers before they can board the Ebon Hawk
Get your first Dark Side points
Complete the Prologue