1. How are you doing?

Question

2. How are you feeling?
3. How is it going?
4. How are you?
5. How do you feel?
6. How are you today?

- I feel delighted.
- I feel happy.
- I feel satisfied.
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Are the questions all the same? Can we answer as in the above?

Answer 1

Yes, they all mean much the same thing, and they can be answered with any of the three possible responses. One might also say, "I feel terrible!" :)

Answer 2

Yes, the questions are all fairly standard ways to greet other people.

The replies are usually one or two words --
Oh, fine
Okay
Just fine
Doing well
(And others)