What you are referring to is called self-porting and should be discussed with an attorney in a private consultation.

(Applicant threatened and told he would be banned from United States if he didn't sign a paper)

What paper was signed? More information is needed.

Can I move back to Employer X? ( he has not revoked my visa ),Does Employer X has to file anything with immigration?

These issues should be discussed with the company attorneys because of the sensitive deadline.

Can a parent of a US born child living in Canada obtain custody of that child.

Was the court judgment made in Canada or the United States?

Can I Apply EB2 Green Card in OPT ?

There may be issues with extending your OPT because filing an I-140 shows immigrant intent.

Can my wife apply for change of status from H4 to F1 if she made a trip out of US in last 30 days ("Preconceived intent" ???)

When she was last admitted was she asked about what she plans to do in the U.S.?

8 weeks and still have NOT received the USCIS receipt number !!

Do you have proof of delivery? You can call USCIS and ask for the number.

What is the process of I94 at port of entry? How to have electronic version on cbp.gov reflect right date of 12/31/2017?

You will need to submit your current I-94 that is valid until 12/31/2017

Hello. My question is: Is it true that green card holder can lose status after applayng for citizenship and being denied?

Yes, if during the citizenship interview fraud or crimes are discovered.

What are the options for E3 holder to become a green card holder? Or what other options he has to stay longer till he gets anoth

Most people get their green cards through employer sponsorship, investment, or a family member sponsorship.