Can't learn Martial Arts skill

first off is the sim mastered in the marital arts level 10 if so then he/she has mastered it and only need to complete the other parts you can check that in your sims skill journal the other parts are meditate x amount of hours to be ablke to zenaport,  break i think it's 150 wooden boards to earn timber terminator something like that which then you should be able to break a space rock with ease which means then you can fight mummies

the book only teaches the first steps of martial arts and is no use after that you could try a couple of things first have the sim in everyday wear then see if he/she can use the boardbreaker or training dummy ( it may one of the martial arts suits could be corrupted so if the sim can change to an martial arts outfit and still train then one of the other suits is not working right to fix that send the sim while in everyday wear to a dresser plan outfit then delete the extra outfits if they have more than one martial arts outfit )

or you may need to reset your sim to reset the sim ctrl+shift+c hold all 3 together in the menu bar that appears at the top of the screen type resetsim first name last (of your sim ) hit enter for example my sim is named John Dear i type in resetsim John Dear

or  a save game corruption could be happening if your traveling then wait until your back in the home world then from edit town move the sim out and back in then once you move your sim back in save the game with the save as new name for the save, at worst while in the home world  go to edit town save copy of your sim to the library and star anew game with the sim and see if they can skill up again