Hitting an enemy with a lightsaber throw in Jedi: Fallen Order takes some practice. You’re going to find a handful of enemies that can survive a single hit, but there’s an achievement called Triple Take you get for taking out three enemies with a single throw.
To complete this achievement, you need to acquire the Lightsaber Throw ability in the lightsaber skill tree. It also helps to have Power Throw skill, extending how far Cal throws his lightsaber.
The best way to get this achievement is to revisit Zeffo or Kashyyyk. These planets feature the most Imperial activity, giving you the best chance to run into the weaker stormtroopers. These are your best targets for completing this achievement.
You want to spend time finding a small cluster of the basic stormtroopers, ranged or melee. Having a combination of both might be better. When you get at least three of them in a small group, do your best to find a tiny alleyway or choke point to herd them into to keep them clustered.
When they start attacking you, aim for the stormtrooper in the back and then toss your lightsaber at them. Your lightsaber is going to fling out, eventually hitting the person in the back. Because it’s active while in flight, you should also hit the other two stormtroopers in the process.
This technique worked extremely well against the ranged stormtroopers because they preferred to stick closer together and stayed at a distance. Melee troopers are more inclined to run up to you to fight, possibly interrupting you or ruining your chance to get all three.