these are system classes that are part of the product that do exists in the new installed version in the %SYS namespace.

If the Studio screenshot you have posted is not from the %SYS namespace (it really does not seems so), then probably the System package is mapped to that namespace, possibly also the related globals. But...I'm guessing here from the little details and context you provide.

If %f is not working in your environment my guess is that, for some reason, the property OriginalFilename is not set in the incoming message to your EnsLib.File.PassthroughOperation Business Operation.

Where is the incoming message coming from? Why the OriginalFilename  is not set?
Can you provide some more details on your environment?

For your response I assume you are searching for a class used by a Business Host component within a production.

Using IRIS you can search for that, and much more, using "Interface Reference" within the Management portal:

Unfortunately you are using an old version where this feature is not available.

Add this to the (possibly long) list of good reasons to move to IRIS.