How do you find out your dharma or purpose in life??
There's not necessarily a final answer that you can get in one fell swoop and be done with it. But there's a direction. As long as you are incomplete, limited by delusion, unable to express continuous love, subject to unhappiness, subject to suffering, subject to conditions — as long as this is the case, there is a direction in which to move. Regardless of where someone is at, whether they are immature or advanced, we all share a correct direction as long as we labor under the delusion of selfhood.
If you know your purpose or direction, only do it.
If you don't know your purpose or correct direction, your purpose is to find out.
Keeping the question "what is my correct direction, what is my life for?" is most important. It's not that you expect some simplistic, dogmatic answer to sum it all up (though if it hits you you may exclaim "Oh, so simple!"); but keeping the question, the sincere effort to look into the issue, works on you. It clarifies your life. Everything that happens to you becomes reflected in the question; you learn within its context. Thus, wisdom develops.
Seeing examples and living with role models of correct direction is also extremely influential on your understanding. You may have an intellectual knowledge that your life shouldn't be wasted; but that knowledge may not have a living expression in your heart and in your daily activity. To live among those who do express correct direction from moment to moment is extremely valuable. You can connect the dots between their stable devotion and confidence, and the decisions and practices you undertake.
Finally, there is no better clarifying condition than awareness of impermanence, awareness of death. Death contemplation and death meditation are renowned across many cultures and spiritual traditions as the most crucial practices for clarifying life direction.
Included in this awareness of the absolute certainty of death and the uncertainty of its occasion, we might also specify the component of 'fear of Samsara' as a motivating factor. In general, we lack correct direction and spiritual motivation because we still have the illusion that we can work things out within Samsara; i.e., that if we gather enough possessions and opinions, or the right relationships and accomplishments, we can be happy with a realm that is — by its very nature — not satisfactory. We don't really recognize and tremble appropriately at our extremely tenuous position and the vast, endless suffering that awaits us if we don't get clear.