Normally you would just use the Help/About link in CA Process Automation to get the full version and build information.
However when PAM is down, this option is not available.
We are still able to get the full version information, although there is not a "version" file for the PAM installation.
You will want to have something like WinRar that can open (not extract, just open) a jar file.
In the \PAM\server\c2o\ext-deploy\c2oear-snapshot.ear folder is the c2oserver-snapshot.jar file. Using WinRar to open the jar file you will see the MANIFEST.MF file. In that MANIFEST.MF file is the version of CA Process Automation.For instance: Implementation-Version: 4.2.500CP01
which indicates 4.2 SP02 with CP01
CA Support will be glad to assist in getting the information for you if you find you are having problems.