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