I am working with a man who appears to be about 70. He remembers his name and where he was born, but not his birth date. He knows a name for his mother, but does not know if it is her first or last name. How can I prove his identity?
My first recommendation would be to go with your client to the local SSA field office with whatever information you have been able to verify and that he is able to report. SSA can sometimes find someone's Social Security number with their name, DOB and parent's information. It often depends on how unique their name is and how easily they can narrow it down. SSA has a special provision to establish a new SSN for folks who are unable to identify themselves by reason of homelessness, amnesia or mental impairment.
The explanation in the SSA Program Operations Manual is at the following link: https://secure.ssa.gov/apps10/poms.nsf/lnx/0110210120!opendocument
You will want to talk to the local SSA office about taking the steps to go through this process if necessary.