Q: how to recover lost files from emptied  trash mac G4 power book

Either from your backup or from an (expensive) data recovery service.

https://discussions.apple.com/docs/DOC-1689

1. The screenshot shows how to "undelete" a file. It will be moved back.

If you simply put files in the Trash you can restore them by opening the Trash (left-click on the Trash icon) and drag the files from the Trash to your Desktop or other desired location.

2.   "Time machine" is a built-in backup tool that works with your Mac and an external drive, As the problem you described, I read it.  The files deleted in Trash bin could be a different problem which Time machine can't solve.  you can read this article and learn more. I hope it will help.

3. If you don't have a Time Machine backup yet, then your best option would probably be uFlysoft Data Recovery for mac software