That's a huge question but your answer can be simple and general rather than very specific.
Your answer might be that you'd like to work with children, or animals, or the elderly in some way, for example.
Picture your 'perfect' life: what does it look like? Is there a spouse, children, pets? Are you living on a farm, a mountaintop, a bustling city, a quiet beach town? In this life have you achieved a desire to.. paint, play the piano, tend a garden, volunteer in a soup kitchen or a school? In this life are you single and financially independent and travelling for pleasure?

It might feel like you are being asked to make decisions that are concrete and can not be changed, but in truth life begins at one point and often changes as we change and grow as we go along. So it's okay to choose a beginning point for now. You may choose many beginning points in your life as you decide to change directions as your interests emerge and evolve. Right now, this is an "Okay, let's start here..."

I think it must be very wonderful to have someone like your T interested in seeing you realize what you want in life.