"What do you want to do?"
Translation:Vad vill du göra?
The verb and the subject go together. Despite sounding similar, du means you, not to do, which is göra.
Vad vill du göra? What want you to-do
The position-II rule says that questions that are not yes/no questions (amongst other types of sentences) will always have the verb in the second place, so since the question word vad 'what' takes up the first position, automatically the subject will take up the third position. So vad vill göra du can't work because the subject needs to be next to the verb.