For example, if I cannot understand what you are saying, I may say “What talking you?

比如说，如果我没听懂你在说什么，我可以说，“What talking you?”

youdao

What do you mean by talking like that to me?

你那样对我说话是什么意思？

youdao

I don't understand what you are talking about.

我不明白你在说什么。

《柯林斯英汉双解大词典》

I don't even know what you're... How... What are you talking about?You want me to go away? I can't...

VOA: standard.other

What I am talking about today, I will not be testing you, but maybe you might pay attention because about a month from now we will ask you a few skill testing questions about it.

我说的是今天，我等会不会测试你，但是你可能会重视了,因为一个月之前,我们问了你关于一些测试的技能。

麻省理工公开课 - 固态化学导论课程节选

However, your friend might think that what you're talking about is more important than the project that you're discussing.

然而，你的朋友可能觉得你们谈论的内容比项目更为重要。

There is 课堂 - SpeakingMax英语口语达人

And you never want to be in a conversation where the person you are talking to has no idea what you are talking about.

FORBES: 'I Have No Idea What Your Company Does!' Five Steps To Clearly Explain Your Startup Idea

Before you deliver a message, whether it is to a large audience or just a few people, think through the strategy of how to make what you talking about a reality, and how you will get people excited about doing that.

FORBES: Mr. President: Speeches Are Not Plans -- or Strategies

Most Americans have no idea what you are talking about when you say FATCA, and neither to the citizens of the countries that are signing these IGAs.

FORBES: FATCA Makes Foreign Banks Report Americans