1
What are you doing this weekend?
To sign this, you would sign 'WEEKEND', point to the person for 'YOU', and then use the 'do' sign while furrowing your eyebrows to indicate a 'what' question.
2
What do you want to do?
Sign 'YOU', then 'WANT', and finish with the 'do' sign. Remember to furrow your eyebrows at the end to show that you are asking a question.
3
I don't know what to do.
Point to yourself for 'I', sign 'DON'T-KNOW', and then use the 'do' sign. Your facial expression should look puzzled or uncertain.