They will ask the reason for your travel and what you are going to do in the country

Questions like: what are you going to do in the United States? Where will you stay? How long will you stay? They will not ask how long you will stay if you have immigrant visa

Better to have all your documents with you to prepare for any questions

I think nonimmigrant visa will get more questions than immigrant visa because they want to make sure you will return back to your country