That’s not looking good, usually on a bad sector the drive will write it to a spare sector transparently and mark it as bad internally. That means they’ve probably all already been used up.
smartctl should work just fine over USB, unless your USB adapter for the drive is really bad. Make sure you’re using sudo as well. Worst comes to worst, try using it in a different computer.
Your next goal would be to get it to do a full self test with smartctl. A low level format might help clear some bad state and it might be okay afterwards with a fresh format accounting for whatever defect it built up over time.
I wouldn’t recommend it. It might work for a bit and then just die completely.