From the legion talent calculator (
http://legion.wowhead.com/talent-cal.../assassination ) on wowhead, i would say, looking at the spells each class learns before lvl 10 (for example, if you choose Assassination in the calculator, you can see that you learn Mutilate at lvl 1 and then poisons and Envenom while no other spec has specific skills before lvl 10; Beast Mastery learns Kill Command at lvl 3, etc) :
DK : no idea, maybe Unholy since you start with a 2-handed weapon
DH : Havoc
Druid : Feral
Hunter : Beast Mastery
Mage : Frost
Monk : Windwalker (or Brewmaster)
Paladin : Probably Ret
Priest : Shadow
Rogue : Assassination
Shaman : Elemental
Warlock : Affliction
Warrior : Arms