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