However, if you open only one file at a time, then the topmost item of the “Recent” menu always corresponds to the open file.
You can get the file path with this:
tell application "System Events"
tell process "Audacity"
tell menu bar 1
tell menu "File"
tell menu item "Open Recent"
tell menu "Open Recent"
set mostRecentFile to name of menu item 1
end tell
end tell
end tell
end tell
end tell
end tell
Then you can further process the mostRecentFile
variable with KM or AppleScript…
(In this form the script works only if a file window is open.)