If it is brown 'stuff' that is scraping off then this will be due to the build up of body oils from hands on the steering wheel ( a common problem). Difficult to tell this from the photo though, It will need degreasing and then refinishing and protecting so that it doesn't happen again.
Steering wheels are notoriously difficult to deal with and are the prime example of why a protector should be used from the start - this would stop this problem from happening