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