If you have backups enabled under Preferences > General, period backups will be saved of your work. Where they are saved depends on the operating system.
Generally you can locate the autosave folder by selecting File > Recover Backup. If for some reason that doesn't work, however, you can manually navigate to the backup folder:
To manually go to this folder from the Recover Backup dialog, enter %APPDATA%\Fade In in the Filename text field. (To go to this folder in the File Explorer, click in the address bar to paste the path.)
/Users/<Username>/Library/Application Support/Fade In
/Users/<Username>/Library/Containers/com.generalcoffee.fadein/Data/Library/Application Support/Fade In/ (Mac App Store version)
To manually go to this folder from the Recover Backup dialog, first press the forward slash (/) key (or Command+Shift+G) then copy and paste the appropriate path as per the above, replacing <Username> with your own user name. You can use "~" to stand in for "/Users/<Username>", as in "~/Library".
To go to this folder in the Finder, choose Go > Go to Folder from the Finder menu.
Note that the user "Library" folder is typically not visible in Finder, so you can normally not browse directly to it and will have to enter the full path as per the above.