When do Rogues learn Garrote?

Rank 1 at level 14, with later ranks at 22, 30, 38, 46, 54. Visit a class trainer in any capital.

Did Garrote change from Classic?

No recorded differences from Classic 1.12 in this snapshot.

Rank	Level	Cost / range / cast	Effect	Classic 1.12
Rank 1	14	50 Energy · Melee Range · Instant · Requires Stealth	Garrote the enemy, causing 144 damage over 18 sec, increased by your Attack Power. Must be stealthed and behind the target. Awards 1 combo point.	same
Rank 2	22	50 Energy · Melee Range · Instant · Requires Stealth	Garrote the enemy, causing 204 damage over 18 sec, increased by your Attack Power. Must be stealthed and behind the target. Awards 1 combo point.	same
Rank 3	30	50 Energy · Melee Range · Instant · Requires Stealth	Garrote the enemy, causing 282 damage over 18 sec, increased by your Attack Power. Must be stealthed and behind the target. Awards 1 combo point.	same
Rank 4	38	50 Energy · Melee Range · Instant · Requires Stealth	Garrote the enemy, causing 354 damage over 18 sec, increased by your Attack Power. Must be stealthed and behind the target. Awards 1 combo point.	same
Rank 5	46	50 Energy · Melee Range · Instant · Requires Stealth	Garrote the enemy, causing 444 damage over 18 sec, increased by your Attack Power. Must be stealthed and behind the target. Awards 1 combo point.	same
Rank 6	54	50 Energy · Melee Range · Instant · Requires Stealth	Garrote the enemy, causing 552 damage over 18 sec, increased by your Attack Power. Must be stealthed and behind the target. Awards 1 combo point.	same

Blood Splatter (Assassination row 3): Increases the duration of your Rupture ability by 6 seconds and your Garrote ability by 9 seconds.
Opportunity (Subtlety row 1): Increases the damage dealt by your Backstab, Garrote, Ambush, and Mutilate abilities by 20%.
Dirty Deeds (Subtlety row 2): Reduces the Energy cost of your Cheap Shot and Garrote abilities by 20, and your Garrote ability no longer requires you to be behind your target.
Initiative (Subtlety row 3): Gives you a 100% chance to add an additional combo point to your target when using your Ambush, Garrote, or Cheap Shot ability.
Ghostly Strike (Subtlety row 4): A strike that deals 125% (180% if a Dagger is equipped in your Main Hand) weapon damage and increases your chance to dodge by 15% for 7 sec. Awards 1 combo point. Also causes your next Ambush or Garrote cast within 7 seconds to not require Stealth.
Hemorrhage (Subtlety row 5): An instant strike that deals 100% weapon damage (145% if a Dagger is equipped) and increases the damage of the caster's Rupture and Garrote abilities by 15%. Lasts 15 sec. Awards 1 Combo Point.
Death Mark (Subtlety row 7): Finishing move that marks the target, storing a portion of the damage dealt by your attacks per Combo Point. Garrote and Rupture damage is stored at twice the rate. After 6 sec, the stored damage is dealt up to a maximum increased by Attack Power and Critical Strike chance.

Source: beta client 1.60.1.70753. Spell ID 11290.