"Stream of consciousness" is when we get the unfiltered thoughts of some character. Usually, that's a pretty complicated and confusing style. You have lots of run-on sentences, sentence fragments, and strange digressions. It's all meant to copy the way a character's mind (consciousness) would work. For an example of some difficult stream of consciousness, check out William Faulkner's As I Lay Dying.
And here, we do get Tris's thoughts in the moment. (Check out "Narrator Point of View" for some thoughts on that.) There are some run-on sentences and lots of sentence fragments. But generally speaking, this style is a little easier to read (just a little) than Faulkner or Virginia Woolf. One benefit of this "Tris-style" stream of consciousness is that it keeps us close to Tris's thoughts, so we can see how they change and affect her. For instance, when she goes to see Al's body after his suicide:
Christina's hands get tighter and tighter around my arm. I should tell her to let go of me; it's starting to hurt. Someone kneels next to Al's face and pushes his eyelids shut. Trying to make it look like he's sleeping, maybe. Stupid. Why do people want to pretend that death is sleep? It isn't. It isn't.
Something inside me collapses. My chest is so tight, suffocating, can't breathe. I sink to the ground, dragging Christina down with me. The stone is rough under my knees. I hear something, a memory of sound. Al's sobs; his screams at night. Should have known. Still can't breathe. I press both palms to my chest and rock back and forth to free the tension in my chest. (24.15-6)
Check out how the sentences start out complete and even a little complex—look, that's a semi-colon in that second sentence and it's used correctly. (People rarely use semi-colons correctly when they're in pain.) But then the sentences start to break down: we get fragments ("Stupid") and repetitions that make it seem like she has trouble moving on to the next thought: "It isn't. It isn't."
But that second paragraph is where the pain of Al's suicide really destroys Tris's grammar and her sense of the world. "My chest is so tight, suffocating, can't breathe" isn't grammatically correct; and notice how she shifts from the important stuff around her (Al is dead) to sensations that aren't so important, like noticing that the stone is rough. People under pressure notice the weirdest things.
If you ran this book through a computer analysis program (beep boop beep), you might find that the most used phrase here is "I am" and the most used single word is "maybe." Or at least, those would be our educated guesses.
That is, most of Tris's sentences are super straightforward and pretty easy to read: "Will doesn't argue with me" (19.47); "Oh, I think" (25.101); "Slowly I nod" (31.84); etc. We could pull out many more quotes, but you can see from these examples how Tris usually narrates in a straightforward way, telling us what happens without too much flash and flair.
But let's also acknowledge that Tris says the word "maybe" a lot, especially when she's discussing her feelings and thoughts: "Maybe I do mean it" (10.78); "Maybe the answer is neither. Maybe I am wired like the Divergent" (24.88); etc. So Tris might be straightforward in general, but she doesn't seem so certain about her feelings, which really comes out in her style of offering these possibilities.