My Social Security Disability benefit is being garnished for because of a 30 year old student loan that in default. I have been told that there provisions for requesting debt forgiveness. How do I make application for this?

Who do you owe? The government can't take more than 15% and your benefits can't drop below $750

As far as I understand the law, student loan debt forgiveness (federal) only applies to those who have been paying on schedule. The debt is forgiven after 25 years.

I have a 35 year old student loan in default. I have been in receipt of SS Disability Benefits for the last 15 years and The Social Security people have been taking 15% off the top for the last 15 years. In a way, you can say that the loan is being serviced. Following the world financial melt down of '08, my financial situation changed to the extent that my income, minus the garnishment,places me below the Federal Poverty Level. It is my understanding that there are allowances for a party in my financial condition to petition for and receive forgiveness on the debt. My question remains the same. Does anybody know to whom or what office does one contact to petition for debt forgiveness?

Yes, you have been paying for 15 years, but not 25.
I found a proposed bill that is still in committee:
H.R.1330 - 113th Congress (2013-2014): Student Loan Fairness Act | Congress.gov | Library of Congress
But it doesn't appear to apply to you.

I found this. You will have to do your own calculations unless you want to reveal all required info here.
http://www.finaid.org/loans/ibr.phtml

joypulv... Thank you for your post. Not being able to contact you directly, I will be discreet with personal information. I am head of household, disabled, married with 1 minor child. Spouse does not an outside income. Total household monthly SS benefit is slightly less than $1,500 USD. Medicare Part B burden is $108.50.

You clearly fall in the group that could pay zero, but what isn't clear (to me) is whether you are going to be forgiven now when you didn't make any payments for the first 20 years. You are going to have to contact your lender, according to the second website.

Thank you joypulv... following the http://www.finaid.org/loans/ibr.phtml site, I was able to get to [url=http://www.finaid.org/loans/troublerepayingdebt site and it had the necessary information. To quote verbatim, "Total and Permanent Disability Discharge. If a doctor certifies that the borrower is totally and permanently disabled, the loan will be subject to a 3-year conditional discharge. At the end of this period the loans may be permanently discharged. " I'm quite sure that I have met the requirements. Also, there is a financial hardship provision. Thank you very much for your help.

I hope you are right!
Somewhere at the beginning of all this is a requirement that you have to have been paying all along. Gov't programs are always full of conditions. Let's hope I'm wrong...