Nín ɡuì xìnɡ?

您贵姓？  

What's your family name?

Notes:

您(nín): you(respectful)

贵(ɡuì): respectful

姓(xìnɡ): family name

*It's a very polite and formal way to ask other's name. Chinese people often use it when visiting the company.

Example:

A: 您贵姓？

     Nín ɡuì xìnɡ?

     What's your family name?

B：我姓王。

     Wǒ xìnɡ wánɡ.

     My family name is Wang.