The correct option is
B What / do
The correct answer is Option B.
WHAT is used when we ask of some thing or any activity.
DO means 'perform a task'. It is in the simple present tense. The given sentence is also in the simple present tense.
Hence Option B is the correct answer.
The remaining options are incorrect because:
Option A: HOW is used to ask manner and DOING is the gerund/participle of DO (the use of which is not relevant in the given sentence).
Option C: WHERE is used to ask about PLACE. DOES is the 3rd person simple present tense. YOU in the sentence is 2nd person, which means DOES is the incorrect verb.
Option D: Irrelevant to the meaning and context of the given sentence.