It means
What is your best friend like?
"Como era Tu mejor amigo" translates to "What was your best friend like?" in English.
¿Quien es tu amigo? means "Who is your friend"?
Su / tu / vuestro (a) mi mejor amigo (a) = Your best friendyour my best friend (an illogical sentence)If you meant: 'You're (= you are) my best friend' - Es / eres mi mejor amigo (a)
In Spanish, it means "What is the name of your best friend?"
What is your best friend like? (the best friend is female)
This means "How is your best friend?" This is asking about the permanant characteristics of your friend. You might say "Es muy simpático y guapo". If you were to say "¿Cómo está tu mejor amigo?" you would be asking about his temporary condition. "Está bien", "esta enfermo", or some other statement of condition would be a good answer.
Quien es tu mejor amigo(a) ---- as an affirmation, not a question
You would say Te Amo mi amigo or Te Quiero mi amigo
they are asking. What is your friends email address?
que le gusta hacer a tu mejor amigo
Which is you're best friends email address?
Yo cumplo 1 de agosto