Right. It is not a "render" file that needs to be located. However, it SHOULD show up within the Event, in your Browser window, with the unique Compound Clip icon. THIS is where you can select the CC, and create a copy with new parent, e.g. so that you can make changes to the copy without touching the original. This is useful when you work out an effect or title that you like and want to re-use it in different sequences ... while keeping the original as a "template."
BTW, in the old FCPX 10.0.9, before the new Library/Projects and Snapshot structure ... I was using Compound Clips to "version" my edits, by making an edit I liked into a CC, then making a "new parent" copy and editing that as the new version. I would eventually export as Master File when done.
However, Oliver and others on this forum warned me off of that practice, noting CC were often unstable when used that way.
I don't know if that is still the case in v10.1.1 -- and I no longer work that way, now that we have the new structure.