Where did Santaigo find the answer on how to turn a man into the wind?
Santiago finds the answer in two places. He finds in in love and in knowing that God is within him, so he is God, and thus, Santiago can perform miracles.
First, Santiago asks the wind for help. There is an argument in which the wind says that he and Santiago are too different to become the same. Santiago says that he wishes to reach all corners of the world, just like the wind. He tries to convince the wind that they are really not all that different. He also tells the wind that love can help any situation - that it can empower the change and help the wind. Finally, the wind is annoyed and feels demeaned. It tells Santiago to talk to the Hand That Wrote All. Santiago agrees, but asks for a sandstorm so that he can look into the sky without squinting or being blinded by the sun.
Next, Santiago speaks to the sun. The argue about knowing and not knowing love. Santiago tells the sun that love can and will transform the Soul of the World and asks the sun to turn him into the wind. The sun cannot (or will not) and sends Santiago to speak to the Hand that Wrote All.
Santiago talks to the Hand That Wrote All, but quiets, and senses he should not speak. Instead, he looks inside of himself and prays reflectively. Santiago then experiences a rush of love. He ralizes that the Soul of God is within his own soul, and that he can achieve miracles. When the tribesmen look to where Santiago stood, he has disappeared. Instead, he is on the far side of the camp. The men are afraid, and the alchemist is pleased.