It's good to know the organs but if you have a general idea, you are still fine (even if you don't know, energy will find its way as Master Lin says). Qigong is message healing. The Qi is intelligent. If you are pointing towards someone's stomach and you want the energy to direct to pancreas, Qi will find its way. Your thoughts, your love, your heart, your intention are most important for healing. Trust the energy, and the consciousness to go where it needs to go.
Think about email. When you email someone, do you have to know where the person is? It will get to the person. Now if you know where the person is, you can give a call and ask to check the email ASAP if you are in a rush.