There is no easy way to this in my opinion. This is one of the reason why you were studying a variety of things during your study in University, i.e. to see which one take your fancy.
Even if you decided to like one thing (mine was Virtual Reality), when you start your professional life (when you start working and earning something), situation might change and you might discover something else you didn’t know previously.
Or even worse, you might not get a job in the area that you wanted to work on, you were forced to start a job in a completely different area. For me it was Financial Software, which I am still doing to this day.