Clearly any given piece of literature is going to employ literary and rhetorical devices as part of their attempt to depict scenes and character, and this text is certainly no exception. In this incredibly rich text, the author asks us to imagine a supposedly perfect world, and then challenges us with its utilitarian manner of achieving that perfection, and asks us whether it is worth it. However, along the way, many literary terms are used in describing the kind of perfection of this city called Omelas. One of my favourites is a simile describing the priests and priestesses ready to "copulate" with anyone as part of their worship of the god of Omelas. Note how they are described:
Surely the beautiful nudes can just wander about, offering themselves like divine soufflés to the hunger of the needy and the rapture of the flesh.
The simile obviously strikes a wryly sardonic note at our need to imagine some kind of orgy to make this city more believable.
Consider too the imagery employed to help us picture the scene of the opening of the Festival of Summer:
A marvellous smell of cooking goes forth from the red and blue tents of the provisioners. The faces of small children amiably sticky; in the benign grey beard of a man a couple of crumbs of rich pastry are entangled... An old woman, small, fat, and laughing, is passing out flowers from a basket, and tall young men wear her flowers in their shining hair. A child of nine or ten sits at the edge of the crowd, alone, playing on a wooden flute.
Note how the author here combines as many of the five senses as possible to bring this scene to life and to help us as readers see, smell, hear, taste and touch the scene that she is bringing to life.
Hopefully these examples will help you to revisit the story yourself and find more literary and rhetorical devices of your own that you can comment on. Good luck!