See:
The easiest way to check is probably the Exchange Setup Logs
Open those up and look for this command either false or true
ActiveDirectorySplitPermissions True if enabled, False if not
Setup.exe /IAcceptExchangeServerLicenseTerms_DiagnosticDataON /PrepareAD /ActiveDirectorySplitPermissions:True
If you dont see that switch used, then you are using the default shared perms model
You can also use this as a guide: