How can I make use of info from a `file-bookmark` entry in a plist?
The data in file-bookmarks can be converted to an NSURL object.  If you know at least a little about macOS programming, you can load this data using the UserDefaults system and parse it back into a path using NSURL's URLByResolvingBookmarkData method.

There is some Objective-C sample code over at StackOverflow that still works on Mojave, reading data from FXRecentFolders and outputting the path to stdout.  I am not skilled enough in Swift, but it is probably not difficult to convert that to some equivalent Swift.