We have lots of wooden knob puzzles in our house. Right now, my oldest daughter is no longer interested in them because they are too easy and they are still a little too difficult for my youngest daughter. For a new activity, I turned the pieces into magnets for my youngest daughter to practice using the knob pieces.
For the activity I used a metal pan and taped on a landscape photo. Even better would be to match the photo to the group of pieces (a farm photo for farm animals, etc). I demonstrated how to pick up one piece using the knob and attach it to the pan. Using the knob was a new skill for her, as she naturally went to grab the entire piece. She quickly caught on and has been using the knobs ever since. These types of knob puzzles are very good for developing the pincer grip which is needed for writing and drawing as they get older.
To make the pieces magnetic, I securely duct taped a magnet on the back of each piece.