Penelope Trunk has an excellent post about passion and work. She nails it when she says:
When you say you want to do something you’re passionate about, you really mean, when you think about it, that you want to do something that is right for you. Something that is fulfilling and feels like the thing you should be doing with your life.
She goes on to briefly detail why it is schools teach us the opposite of this.
As usual, this post is well thought-out, well researched, and well written. So, if you're curious about what it really means to be passionate about a job, read her post and then think about what engages you most.
What skill do you possess that you're great at doing? That you can do well almost without thinking? When do you have control over your work? When can you see your work making a difference?
Figure out what you need in your life to be fulfilled. Find that work. Then, as long as you have control over your hours and you can see how you help people, you will feel good about your work. And you know what happens when people feel good in their work? They stop asking themselves bullshit questions about what they are passionate about.