HOW TO ASK AN INTELLIGENT QUESTION?

I hope someone can help me with my question

I want to ask a friend why is she practicing a certain musical piece at her friend’s house. I don’t want her to tell me “why” she is practicing the musical routine but instead I want her to tell me what is the routine for. Is it for a Fifteen, a Birthday party? I don’t know how to ask the question. I came up with a couple of questions myself but I’m unsure if they are correct.

1. For what you are going to be practicing at her house tomorrow?

2. For what you are going to be practicing at her house tomorrow?

OR

3. Why are you practicing the dance routine?

4. Why are you practicing the dance routine at her house? (By adding "at her house" those the meaning of sentence changes"?)