Should a green card holder file a tax even if he is not working in the US for a while?

You're putting your green card in jeopardy if you stay out longer than 6 months. And you should always file your taxes.

I am applying for a Change of status from B1 to F2, my wife is in USA on F1 visa. Do I need an I-20 before I file for I-539?

The I-20 goes to the student, not the dependent class. You need to study the instructions to the form you referenced to see what evidence you need...

Who is the petitioner in the immigration case, I or my husband (he is an American)

The petitioner is your husband. Whether what you submit would be sufficient would depend on what was requested. You should contact an immigration...

Should I Enter US Using B1/B2 or Wait for F1?

You would be better served if your B1/B2 is already annotated as a prospective student. If that is the case, then you are in good shape. But even...

File Form AR-11 when you move to inform USCIS that you have a new address. You can do that online as well, and it costs nothing to file.

Can My employer apply for Green Card with out being on H1B status.

The path to the work-sponsored green card is tortuous. That is why you may have been encouraged to seek the H-1B visa first so that you can...

My Husband had his immigration interview on the 18 January 2015 in Pakistan. in the interview the ask him for joint sponsor and

You may have to wait a bit to know whether what you newly submitted would satisfy the AOS requirements. It depends on the size of the household...

Can another employer sponsor my greencard while I am on H1B?

Depends on whether this "new business" has an ability to pay you. That must be demonstrated to USCIS' satisfaction. There must be an employment...

My F1 expired but I am currently enrolled in my second masters. What status do i come under?

F-1 or else you couldn't have started your courses, or there was a massive blunder on the part of the DSO of your school.

Can I leave the US in between jobs once the H1B visa transfer is approved?

As you would still be employed by Company A, it should be possible. But you should talk to Company B's lawyer to see what exactly you might be...