Tell me . . . . . . you have put my hat. A. which B. what C. where D. whom

The correct answer is where.

• Which is used to ask about a specific person or thing from a group of two or more. For example, “Which hat do you want?”
• What is used to ask about a general thing or idea. For example, “What is your name?”
• Where is used to ask about a place. For example, “Where is my hat?”
• Whom is used to ask about a person or people who are the object of a verb or preposition. For example, “To whom did you give my hat?”

In the sentence “Tell me where you have put my hat,” the speaker is asking about the location of the hat. Therefore, the correct answer is “where.”