Asking when is somebody's birthday in Korean
The other day, I learned the word "When" 언제.
Now I'm exploring how to use it.

Is it correct to say
언제 그 여자 생일
When is her birthday?

How do I say "When is your birthday?"

Yes, I know everyone celebrates their birthday on the same day in Korea (:

Question

Asking when is somebody's birthday in Korean
The other day, I learned the word "When" 언제. 
Now I'm exploring how to use it.

Is it correct to say 
언제 그 여자 생일
When is her birthday?

How do I say "When is your birthday?"

Yes, I know everyone celebrates their birthday on the same day in Korea (:

Answer

Expression for 'When is her birthday' is  different depending on situation.
 her - adult
   "그 분 생신이 언제에요?" /  "그 분 생신이 언제야?"
 her - younger than you
    " A(the name of her) 생일이 언제에요?" / "A 생일이 언제야?"

For "When is your birthday?"
  "생일이 언제에요?"  / "생일이 언제야?"

Answer

When is your birthday?
생일이 언제예요? / 생일이 어떻게 돼요?
생일이 언제야? (informal)