Надо задать общий вопрос и 2 специальных:

Ann is singing upstairs. She sings very well.

The door opens easily. Peter is opening the door now

1. Ann is singing upstairs.

Is Ann singing upstairs?

Ann is singing upstairs, isn't she

Who is singing upstairs?

2. She sings very well.

Does she sing very well?

She sings very well, isn't she?

Who sings very well?

3. The door opens easily.

Does the door open easily?

Does the door open easily or hadly?

What opens easily?

4. Peter is opening the door now

Is Peter opening the door?

Peter is opening the door now, isn't he?

Who is opening the door now?