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