"What is your name?"
Translation:Come ti chiami?
chiamarsi = to call oneself. SO: come ti chiami = how do you call yourself?
Duo hasn't explained the formal you yet. If you are addressing an adult stranger, the polite way to ask their name is: come si chiama
If one is in a business meeting, a convention or even a shop, it is considered polite to use the formal; until the person tells you it is not necessary.
I also reported this sentence because it popped up in http://www.duolingo.com/word_practice/it/si/Pronoun but it doesn't use "si".