Fill in the blanks with appropriate demonstrative or interrogative pronoun.
_________________ do you wish to meet?

The correct answer is: Whom

The correct answer is "Whom".
Whom do you wish to meet?
Here, the speaker is asking somebody about the person with whom he wishes to meet. To express the question, we must use an interrogative pronoun. Since the speaker is demanding information about the receiver of an action(meeting someone), the correct answer is "Whom".