There is no standard location for EagleFiler libraries. The library is stored in the folder that you chose when you used the New Library… command. Most people choose their Documents folder.
Normally, you don’t have to manually open your EagleFiler library. If Remember open libraries between launches is checked in the settings, when you quit EagleFiler (with a library window open), EagleFiler will automatically reopen it the next time you relaunch EagleFiler.
You can also re-open recent libraries using the File ‣ Open Recent command, the pop-up menu in the Drop Pad, or The Dock Menu.
If you library does not appear in the list of recents, you can find all your libraries by doing a search in the Finder for:
filename:.eflibrary
To move your library, please see the Library Folders section of the manual.