Jacob had the desire and potential to be a pianist but became, instead, a trader in commodities. He decided never to touch the piano again. According to Maslow, what is going on with Jacob?

I would say the answer would be that he was not able to achieve self-actualization. This is the last stage of Maslow's Hierarchy of needs. It is where one achieve and used his talents and capabilities. Another term would be self-fulfillment. Jacob was not able to achieve this since he did not turn the way he wanted to be.