You can say it a few ways: Namae wa? [simple]　名前は？ Anata no namae wa nan desu ka? [formal]　貴方の名前は何ですか？ Anata wa dare desu ka? [who are you?]　貴方は誰ですか？

Hello ;)) What is your name = Anata no onamae ha nandesuka?

You can also use omae, kimi and temee. But they are not a nice way of saying "you" in this context. In example, temee wa dare da? Has a kind of "Who the hell are you?!?"-feeling to it. So don't use it when you ask your friends grandparents names.