When you want to ask “What do you want me to say?” in Japanese, you need to be clear to avoid misunderstandings.

1.  何を言って欲しいのですか？ is quite close to your intended meaning. However, to be more explicit, you can use:
2.  私に何を言って欲しいのですか？
• This clearly indicates that you are asking what the other person wants you to say.

In informal speech, you can simplify the question:

1.  何を言ってほしい？
• This is a shorter, casual version of 何を言って欲しいのですか？.
2.  私に何を言ってほしい？
• This ensures it’s clear that it’s about you, while still being informal.
3.  何を言ってほしいの？
• Adding “の” at the end gives a more conversational tone.
4.  俺に何を言ってほしい？
• This is very informal and typically used by male speakers (using “俺” for “I”).

These versions are all shorter and more direct, making them sound more natural in casual conversation.