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