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.