GetEffectiveRightsFromAcl

[DllImport("Advapi32.dll", SetLastError = true)][return: MarshalAs(UnmanagedType.Bool)]
public static extern bool GetEffectiveRightsFromAcl(
   IntPtr pAcl,
   ref TRUSTEE pTrustee,
   out ACCESS_MASK pAccessRights
);

Microsoft documentation: Link