Do I need any kind of waiver after completing 10 years bar to re-enter since my son is applying for a parent for an immigrant visa?

If you were outside the U.S. for 10 years, the bar to your admissibility has expired, and you should not need any waiver. In any case, no waiver is available to you. If you son files an immigrant petition for you, you will be called to a U.S. Consulate or Embassy for an interview. At that interview, you should have evidence of your physical presence outside of the U.S. for the last 10 years. I you convince the consular officer that you were out of the U.S. for 10 years (and if you have no other problems making you ineligible to be admitted to the U.S.), an immigrant visa will be issued to you. Now, you need to know that a decision of the consular officer is final and cannot be appealed to any court. So, when you go to that interview, make sure that you are as ready as you can be.

No, you will no longer need the waiver. Your son can file the immigrant visa petition on your behalf at this time.

No waiver needed but you will need to show proof that you have been in your country for the 10 years.

If you have been out of the country for at least ten years now since your last departure, you are eligible for entry into the US as long as you have not violated any other immigration laws. If your son is at least 21 years of age, he needs to start the process by submitting an I-130 petition on your behalf. It will take approximately 9-12 months for the paperwork to be processed before your visa interview is scheduled at the US consulate.