What can you do after failing the three attempts for mastering a skill?
How can you master the skill after having failed those three attempts?
Are you talking about testing out of a skill? Testing out of a skill is a shortcut, so if you fail that, it means you don't know the material well enough to take the shortcut. You have to go through the lessons the long way. You don't get points for repeating a lesson because you've already done it and earned the points for it. Does that make sense?
You just continue doing the lesson until you have gathered a set amount of points or gold coins. Just like it takes a specific amount of coins to "learn" a lesson, it takes a specific amount to "master" it if you don't take the shortcut. So, just repeat the lesson over and over until you have actually "mastered" it as it were.