How to revive enemies
Star Wars Jedi: Fallen Order tries to stay as realistic as possible for a game where you play with lightsabers and interact with alien species. This means that you won't see enemies instantly resurrecting after death, just because you've strayed from where you shot them. However, these enemies can respawn in different ways.
The first method of spawning enemies is probably the most common you'll do, which is to die. If you die, the game will reset and you will return to your last checkpoint, whether it's a meditation point or after the game has chosen another random checkpoint. The enemies at this point will have reappeared, which means if you died fighting a group of enemies, get ready to fight them again. It also involves exiting the game and returning to the last checkpoint.
Dying is far from the only method of spawning enemies, as it's usually not done on purpose. The primary and deliberate way to respawn enemies is to seek out a point of meditation and rest. This will regain your health, strength, and health boosts, but will also spawn all enemies. It can be a double-edged sword sometimes, especially if you have to go back to heal yourself after a tough fight, only to then fight them again. For those looking to gain XP, this is definitely the best way to respawn from enemies.
Another way to spawn enemies is to leave a planet entirely in your ship and then come back. This will bring back any enemies you've defeated previously, but it's definitely the most tedious of the bunch, so you'll want to look at the others first.