This is the only knee spin I know about. Both are fairly easy, it will take you about a day to master this move.
1) Get on both knees and hands.
2) Now balance yourself on 1 knee with other leg out to a 45 degree angle and level with your back.
3) Now start to push side ways. Which way to push depends on which leg is lifted. If left leg is lifted push right. Do the opposite if right leg is lifted.
Once you have mastered this move you can do it with no hands (once you have built up enough momentum)