You know it when your heart feels joy in the passion that you have found. What you love to do the most sparks the passion in you and that is what your will is, ultimately you are here because of Love. For what you love makes you happy and happiness transcends reaching others. And the source of happiness comes from Love and God is Love. 1 John 4:8
For through Love incredible things will be done. Therefore search what makes you happy and shine like no other bring forth the light that you have so that others may see the light :)
:) <3
I appreciate you asking this question for I can tell you now that the word of God is waiting to show you what you have been looking for. I don't know what it is but I am compelled to tell you this so dive deeper :)