People usually look for short answers and fast track to their goals. I'm being asked often:
Walid, which topic should I start my knowledge-business with? What topic will bring me more money?
My short answer is always "How to make money/wealth" is your best choice. People will always be looking for ways to build fortune. But this might not be your art.
I always prefer my 2nd part of the answer. You just connect the dots of your life's experiences. Identify your unique values. And start building your brand around this topic. And once you master that topic, not only you'll earn tons of money, but also you'll build a remarkable brand around your lifestyle. You'll enjoy every day at work because you only do what you love.