The following questions helped me: what do you spend most of your free time doing voluntarily? Where do you have a backlog of material that you are afraid of showing to the world? What things do you take for granted because they come easy to you, that others have expressed appreciation or amazement at/offered to pay for?

Also, question your assumption that you need to find 1 thing and devote most of your time to it. Why? What's your goal?

If it's enjoyment, why 1 thing? If it's money, you only need to choose the highest paying profession that you can tolerate.