I know the feeling! I would like to have some jobs, but how to say it... None of them feel like the one career I truly want. I would never be able to put in all the effort I am putting in for my career goal were it any other career.
How I knew that was the career for me? It is a feeling, you see. You read this job's description and at that moment, you simply feel as if it describes you perfectly and as if you just found what you want to do for the rest of your life - you would not mind starting there tomorrow and working there until you retire.
You find yourself astonished; you think 'This job... describes me perfectly!', 'It is everything I have ever wanted!', 'I could do this forever'. And at that moment, the only things you feel are joy, exhilaration, energy, determination, motivation, and a sense of purpose. Then, you do more research about it and try to shape yourself to the job since that job is what you were meant to be.
You start to read books relevant to the job, you look for any internet resources that may help you in that job even though you do not have it yet, you make sure you meet all of that job's requirements, everything.
And no matter how many times you attempt to reassure yourself that is the job for you or try other things to see if you have another passion, your mind always goes back to that job. No other job gives you the feeling you got when you found that job, no other job motivates you to do as many things towards a career as the career which is your dream job. Even if you briefly change your mind, it always goes back to that job, until you realise no other job could be as perfect for you as that job.
This is how I knew what my call in life was. Sorry if this does not help but basically, the gist of it is to read about different jobs, whether they are common or not, and see which one clicks with you.