This is an example sentence from the linguistic course "The Ling Space". They've used this sentence to explain that a subject can shift when we change the sentence.
Just like them in the sentence
Dirk and Jake expect to see them in dreams
can be transformed into this them
"Who do Dirk and Jake expect to see them in dreams?"
But what does it mean?
It's a very strangely written sentence, and not one you would encounter in everyday English (at least, not with anyone I've ever spoken to).
"Who do Dirk and Jake expect to see them in dreams?"
You could break it down this way: Dirk and Jake expect somebody to dream about them (that is, to see them in dreams). The question is asking who this "somebody" is.
In the second sentence
"Who do Dirk and Jake expect to see them in dreams?"
'them' refers to 'Dirk and Jake'. It implies that Dirk and Jake expect someone else to see Dirk and Jake in that other person's dreams; that is Dirk and Jake expect someone else to dream about Dirk and Jake. The question asks who that someone else is.
FIRST
Dirk and Jake expect to see them in dreams
In the first sentence, them refers to some unnamed others (other people or things).
Dirk and Jake expect to have a dream about those people or those things.
SECOND
Who do Dirk and Jake expect to see them in dreams?
them in the second sentence could refer back to Dirk and Jake or to some unnamed others.
If them refers to Dirk and Jake, it could be paraphrased:
Who do Dirk and Jake expect to have a dream in which Dirk and Jake appear?
If them refers to some others, it could be paraphrased:
Who do Dirk and Jake expect to have a dream in which [those people or things] appear?
Those others could be "Mike and Ike", say, or two or more nouns (plane and train), or a single plural antecedent noun, supplied in the context: "chickens, zombies, boats, flowers, mountains..."
