Step 1: Step-by-step transformation:
Move the object 'your work' to the front; convert 'have completed' to 'has been completed' (auxiliary agrees with the new singular subject 'work'); retain 'not' in its passive position; add 'by you' at the end.
Step 2: Result:
Why has your work not been completed by you?
Final Answer:
Why has your work not been completed by you?