Request for personal records

I’d like to pose a hypothetical question:

If an individual had been given clear indication that some sort of investigation of them was taking place, what agencies should they begin making requests and what documents should be requested? This investigation would involve the cooperation of agencies across several states including California (spanning over 4 years). I mention this because this would likely indicate the cooperation of state and federal level agencies.

Also if an individual was declared incapacitated in some way in order to obtain any sort or form of a power of attorney; what documentation would be available to that individual? Consider the scenario in which the individual has not and does not give informed consent nor has the individual received any information regarding the procedure or proceedings.