What can I call you? と What should I call you? と How can I call you? と How should I call you? はどう違いますか？説明が難しい場合は、例文を教えて下さい。

"What can I call you"

means what name you should address a person by. Could also be said as "what's your name?"

"What should I call you?"

Is a way of asking a person what they would like to be called. For instance they might not like their name and wish you to call them by their nickname.

"How can I call you?"

Means how can you call that person, like by a mobile or a home phone.

"How should I call you"

Also means whether the person would like to be contacted by mobile phone or home phone.

Hope that helps. If I didn't answer your question properly please ask me again.