How to delete ALL notes from Stickies app?
This method works for me at least. macOS 10.14.5

rm ~/Library/StickiesDatabase




Using Automator's Record feature, you can ease repetitive tasks. 


First get a new workflow. Then hit record button on the top right. This makes a floating record bar with a stop button and gives focus to Finder. 
Click the Stickies in the Dock and click the stop button in the Automator bar.
This opens Automator with a single action in a block, Running which gives focus to Stickies/ or opens it. 


Now hit the record button and 


Click Stickies in the dock: this opens all the notes.
Hit command+W OR File menu > close note.
Click Delete note in the popup that appears.
Stop the recording.


Now you should have this on your screen.


Click on the "Click "Stickies" in the dock line" in the second block and hit delete. 
You can also increase the playback speed. Now the second block is ready to be copied. So click on the black area to get focus of the same. 


Either right click, hit duplicate. Then use command key to select multiple blocks, right click duplicate, and repeat as many times you wish.





Simply command + click on the blocks and use normal copy paste shortcuts. 





Now save it and run it. When it runs out of notes, it encounters an error, and terminates.