Often times people come to coaching with this question. When I've asked this question, I've learned what is most important is to understand these things:

Who we are is not the same as what we do.
Knowing who we are, our personality, needs, beliefs and values, help us to answer this question in the best of ways.
Just because we know what do with our life does not assure us that the path will be easy or clear at every turn and that we will be filled with unlimited happiness at all times.
Our life purpose remains the same but what we do with our life to express our purpose can change.
When we are clear about our pupose, we can still be unclear about what to do to live this purpose.
When we are clear on our purpose, unclear on what to do, know our beliefs, values and understand our personality, it's time to commit to exploring options.

When you explore this question, what have you learned?