What to say..
How do you say - what is your sister's name?
2 Answers
¿Cuál es el nombre de tu (or su) hermana?
¿Como se llama tu (or su) hermana?
Yes, jphip is correct. To clarify on his answer however, you'd use "tu hermana" when you're talking to someone familiar, such as your friends. You'd use "su hermana" when you're talking to someone who is older than you or a person that you'd like to show respect for, such as a teacher.