To decide if you're passionate about something, consider . . .
Going to school for it
Enlisting in the military
Volunteering in that field first
Getting certified in it
Attending workshops or conferences related to that interest.
Talking to others who are already involved in that field.
Spending time researching and learning more about the subject.
Reflecting on how much time and effort you are willing to invest in pursuing this passion.
Assessing how fulfilling and rewarding it would be for you to work in that field long-term.