What is the difference between "Do you want to eat xxx tomorrow" and "Will you want to eat xxx tomorrow", and which is correct?
Both are correct.
"Do you want to eat xxx tomorrow?" Do is the present tense, and is being used in a question about the listener's present desire (i.e. what he or she wants today, regarding tomorrow).
"Will you want to eat xxx tomorrow" Will is the future tense, and is being used in a question about the listener's future desire (i.e. what he or she will want tomorrow). We do not always know what we will want in the future, but a question about a meal tomorrow is likely to get a useful answer. In reality, this is a question about a present desire, but phrased as a question about the future.
The practical result will be the same in either case, as the speaker will know, from the answer, whether to prepare a meal of xxx tomorrow.