Hey Guys My Sith juggernaught is almost level 50.

and then i can unlock the Legacy force choke,

 

and i wanna start a Jedi knight. is it possible for him to learn "leagcy force choke"??

 

(sry. for my English)

Yes, once you complete your class story for any class, all alts get the Legacy Ability in their Abilities panel to put in a hotbar of choice. The only benefit your Jedi Knight won't get is the Legacy Buff that your Sith has already unlocked, because Sith Warrior's Force Might doesn't stack with Jedi Knight's equivalent buff.

 

I have a capped Inquisitor and a smuggler; my smuggler can shoot Force Lightning Storm. Note that because of cooldowns, you only get one shot of a legacy power per Heroic Moment use.

 

My theory as to why the Republic and Empire buffs don't stack is they're actually the same exact ability in the server and the client simply shows the different icon/name based on whether you're playing a Pub or Imp at the time. My Sith Warrior gets the Inquisitor buff, while my smuggler gets the Consular one; I don't have a Consular.

I highly doubt that's the reason or that that's even the case. It would be a bit overpowered to stack two of the same buff. I'll just say a similar game doesn't allow two of the same buff to be stacked either.