Go to all squares with the knight. The disks mark the squares where you was not.
 
The Knight's Tour puzzle very old. Solutions dating back to at least 850 A. D. Interest in Knight's Tours was revived in the 1700's by mathematicians including de Moivre and Euler, and the problem has continued to maintain the interest of puzzlers and recreational mathematicians, who have discovered many interesting properties of tours on boards of various sizes.