What was it you wanted to see me about？

这是一个强调句。强调句型可以有疑问句，包括一般疑问句和特殊疑问句。本句实际省略了 that ：

What was it (that) you wanted to see me about?

what 作 about 的宾语。

陈述句是：It was somehting that I wanted to see you about.

就划线部分提问，变成特殊疑问句：What was it that you wanted to see me about?

还原后；What did you want to see me about?

【翻译】你为什么想见我？

强调句的特殊疑问句式：

疑问词+ is (was) it + that +句子的其他成分，特殊疑问词即是被强调的成分。例如：

Who was it that found your pen in the classroom yesterday?

When was it that the Second World War broke out?

Where was it that you lost your cell phone?

How was it that he managed to get my address?

How long ago was it that you last saw her?

What was it that had made you so sad?　　

Why was it that silver was not widely used as conductor?　　

Which book is it that you want?　　

Whose umbrella was it that you took away?