Don't know what you're passionate about? No problem. Pick something interesting. Pick something financially viable--something people will pay you to do or provide.
Then work hard. Improve your skills, whether at managing, selling, creating, implementing...whatever expertise your business requires. The satisfaction and fulfillment of small victories will give you the motivation to keep working hard. Small victories will motivate you to further develop your skills.
The satisfaction of achieving one level of success will spur you on to gain the skills to reach the next level, and the next, and the next.
And one day, you will wake up feeling incredibly fulfilled--because you're doing great work, work you've grown to love.