what is sb like? how does sb look like? what does sb look like?
1)would you please kindly advise the difference between the above sentences?
2) "how is sb like?" I think there is no such an expression, right?

Question

Answer

Please don't use dictionary abbreviations like 'sb' in 'real' English - i.e. when you are asking someone a question. We don't use them in normal English. 
What is somebody like is asking about them in a general sense. You could answer with what they look like, how big they are, or what their character is.
Your second one is not natural English.
What does somebody look like just refers to what you see. Possibly their size, but usually what their face looks like, and probably what colour and style their hair is.
Yes, you're right. 'How is somebody like' is also not natural.

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