I would like to know which of the sentences is correct , and kindly provide me with brief explanation

How sure you are that is a correct answer?

How sure you are that it is a correct answer?

Why are you doing this research?

Why you are doing this research?

Sincerely yours

Aqil
How sure ARE YOU that it is a correct answer?

and

Why are you doing this research?

Be careful of the word order of the subject and the linking verb in questions.
I guess the first group provided is wrong because every sentence is not indicating a question rather a statement.

It should be, How sure are you that is a correct answer?

You must be confused in using that in the sentences so let me share my viewpoints. The word 'that' in the first sentence is used as a demonstrative pronoun. Just give an emphasis upon pronouncing the word to indicate that you are using it to stand for a noun so the sentence will be effective to your audience. (e.g I need that.) You will notice. That is used to replace a noun for example a pen, a bag or etc.

On the other hand, the second sentence reveals 'that' as a relative pronoun. (e.g The book that she read yesterday was gone.) That is used to relate a dependent clause to the rest of the sentence.

On the next group provided, the first sentence is gramatically correct.
Teachers: We supply a list of EFL job vacancies
I think

(1)"How sure are you that is a correct answer?"

and

(2)"How sure are you that it is a correct answer?"

each asks a different question.

(1) is a question about the particular answer, as opposed to other possible answers, while (2) is a question of certainty.