In all likelihood, you got this game to play through it, and if you're like me, you glanced at the achievement list, saw lots of "kill tons of enemies," and you thought to yourself: "No problem, I'm playing through the entire game. I'll pick it up as I go along."
Now, you're sitting there, like me, wondering where to go with this after completing that story mode since you cannot replay the prologue AND your kills won't carry over to your Sith Master save, nor can you carry them over to that Jedi Temple DLC. That means all of the wonderful solutions you've been reading won't work at all if you want to keep all of your progress. Are the Jedi Temple and Prologue good places for this? Sure, if you haven't started or want to start over.
My personal grinding point for this and all the other "kill with skill" achievements was the Tie Fighter Factory, right at the beginning at the level. You spawn in a hallway with some droids (wipe them out if you haven't grabbed the kill 35 droids achievement; oh yeah, and the droids of my enemies are my enemies so they totally count as kills too), and once you get to the end of this hall, you bust the door open with Force Push, and you're in a room with some rebels and some Stormtroopers. At the far end of the walkway where you enter is an unlimited force powerup.
Force Repulse is where you hold LT and press B and a nice unseen explosion throws everyone away from you. This one has less of an issue with bolt deflection, but you can still reset the yellow talent spheres in Force Upgrades under the pause menu and build them all back up except Defense Mastery to lower your ability to deflect the bolts.
Clear the room which is about 40 or so enemies (nearly 50 if you grab the six droids in the hallway as well; yeah, the droids of my enemies are my enemies). Pause the game. Save it. Select Mission Select, then Tie Fighter Factory, and then Load Previous Save. You'll start at the beginning of that droid hallway. Do it again and again and again until you get the achievement, then pick your next skill, and do it again.
How long will it take? Depends on how many you did during the story since this method at least respects that you probably have some kills on it. Happy grinding.