If you are running on Jupyterlab on linux like me. What I did is went into command prompt and went to my trash folder.
Trash directories on linux are typically
/home/$USER/.local/share/Trash
or
If you deleted something as root (e.g. deleted a file using Nautilus invoked via gksu), it is at
/root/.local/share/Trash
I ended up changing directories to /home/$USER/.local/share/Trash/files and my deleted notebook was there! depending on how you access your backend you could also try /home/jupyter/.local/share/Trash/
ps
If you are having issues changing directories from Trash to files due to permissions dont forget to become root:
sudo -i
then after sudo -i, go up with:
cd ..
and then
cd home/jupyter/.local/share/Trash
cd files
Best of luck,