Consider this quote from the Harvard Business Review.
"People are often successful not despite their dysfunctions but because of them. Obsessions are one of the greatest telltale signs of success. Understand a person's obsessions and you will understand her natural motivation. The thing for which she would walk to the end of the earth."
So the way to know is by looking at what you do for fun. Do you go to orchestra concerts as often as you can? You guessed it, take as many orchestra auditions you can and land an orchestra job (by the way, there are lots of open orchestra positions this year). Do you love playing with children and your preferred non-artist job is as a babysitter? Working in a school of music or opening your own studio will make you the happiest.
What if you realize that in your free time you don't spend much time related to your art? That doesn't mean that you should give it up, but rather that you have to find a way to connect your art with what you do for fun. Spend every minute of your downtime reading? You could become an editor for a music or or a theater magazine. Love to play video games? Maybe you can write music or record voice over for them. Like to write? Be a reviewer of concerts or plays. Love sharing your knowledge but not in front of people? A classical music radio might just be looking for someone like you.
What you do for fun is what makes you different from a lot of people. Knowing what makes you different from a lot of people is how you can find your niche. Finding your niche will bring you more work, and more satisfactory work.