You can try using a data recovery app such as Disk Drill or Stellar Data Recovery. Usually they allow you to try out the product to see if they can discover any files, but you may need to pay in order to actually recover the files found.
If the USB stick was using the HFS+ file system (aka MacOS Extended), then you could try using the paid app Disk Warrior to attempt to repair the file system. However, if there is a hardware issue involved, then DW will refuse to make any modifications.
I would highly recommend you start some sort of backup strategy so you can recover lost or damaged items from a backup. Apple provides Time Machine for free with every copy of macOS.