what's the difference between "how should I call you?" and "what should I call you?" ?
when I want to known one's name, which is the right one, or both?

Question

what's the difference between "how should I call you?" and "what should I call you?" ? 
when I want to known one's name, which is the right one, or both?

Answer

In the case of a name you say: "What should I call you?"  Or What name do you prefer to be called?