I want to ask someone about what he want me to do. which one of the mentioned below is better and grammatically correct?
What would you rather I did?
What would you rather I do?
What would you rather?
The 1st looks the best to me.
If I'm thinking about what someone want to do, what should I say while thinking? Can I say:
What would he rather do?
"What would you rather I do" is correct in the case where you have presented some options (or are just asking 'what to do' more generally) but are yet to take action.
"What would you rather I did [or 'had done']" would be used where you did something already, but then maybe it's being questioned so you are asking the person -- well, what should I have done instead? What would you have preferred that I did?
"What would you rather?" does get used occasionally but I think it's a bit ambiguous. If there are several options I would rephrase that to "[what/which one] would you prefer?"