What information are you specifically interested in?
I want to fetch all the mapping and its mapped identity in a pi server to a excel sheet, but as I referred SDK it is showing that PIIdentity and mapping feature is not yet implemented.
SO can you suggest some other way out
You can use PI System Management Tools (PI SMT) -> Security -> Mappings & Trusts -> tab "Mappings" to export existing mappings to a XML file or PIConfig input script.
If you are looking for a programmatic solution, please have a look at this post from Patrice.
Since you mentioned auditing the PI System, you may be interested in PI Server auditing. The PI Server log can also be a good resource for information who has connected when with what application. Please see my blog post about How to retrieve connection statistics from the PI Server message log using PowerShell Tools for the PI System