I've figured it out. Thanks for leading me in the right direction!
Just in case someone in the future stumbles upon this thread, here's the answer to my own question:
editorial://open/Folder%20A%2fUntitled%20File%2etaskpaper?root=dropbox&command=MyWorkflow
The file: "Untitled File.taskpaper"
The Directory: "Folder A"
"Folder A" is in the dropbox sync folder that omz referenced in his message.