Student or Learner
Wear is a transitive verb, does it mean I must provide a noun after it under all circumstances?
With smooth and soft straps, this watch guarantees you comfort during wearing/ wearing it.
I wonder if I must need to add back the object (watch) after this verb for the above situation.
Yes, you do, but it would be more natural to say '...while wearing it' (in the words of your title).
However, you could also say 'This sweater is so comfortable to wear', so you don't have to follow 'wear' by a noun under all circumstances.