Where can a metaphor be found in The Giver?
If we're looking for metaphors in a novel, we can find them on two levels: either placed into a single sentence, or used more extensively and symbolically.
First, there's the "sentence" level. The narrator might say, for example, "The girl's hair was a nest, a tangled mess fit for a bird." (This is just an example: it's not in The Giver.) In metaphors like this, the writer says that one thing is another thing, but the meaning is only figurative. (In our example, the girl's hair isn't really a nest; it just looks like one.)
If you read through the first few chapters of The Giver, you'll notice the narrator is very matter-of-fact in presenting details and memories, and in reporting dialogue. We really don't see much figurative expression in the narrator's voice or in the characters' speech, so we don't notice any sentence-level metaphors early on in the story.
When you're looking for metaphors, you can also look beyond single sentences and try to find objects or events that represent something bigger in the story -- even if the narrator never says exactly what that relationship is.
Let's focus on an important metaphor in The Giver that pops up in Chapter 3: light-colored eyes. When Jonas's sister Lily holds the baby for the first time, she notices how he has light-colored eyes, just like Jonas does. She calls them "funny" eyes, meaning that they're pretty rare in the community. A moment later, Jonas reflects:
"...he was reminded that the light eyes were not only a rarity but gave the one who had them a certain look -- what was it? Depth, he decided, as if one were looking into the clear water of the river..."
Because both the baby and Jonas have light-colored eyes, which reveal an unusual depth, and because they're considered odd by other members of the community, we can take a good guess that the baby and Jonas are connected in some meaningful way. We can also surmise these unusual eyes represent something bigger; that is, they're not just eyes: they're probably a metaphor for how Jonas's difference, for his ability to see things differently than other members of the community do.
This guess about the meaning of the eyes gathers support when Jonas is chosen as the Receiver, in part, specifically because the elders noticed his unusual eyes.
So, the light-colored eyes in The Giver are a metaphor for the idea of seeing differently or seeing beyond what others see.
To explore other metaphors in this novel, consider what bigger ideas might be presented by the hair ribbons that the girls wear until a certain age, or by the perception of the world as black and white vs. the perception of colors, or even by the baby Gabriel himself. That is, look at the important objects in the world of the story, and see if they're connected to some bigger ideas within the plot. It's one way of finding metaphors important to the novel and not just sentence-level metaphors.