I'll give a serious response after I figure out what the heck you mean by Pi. (I iz noob.)
Pi stands for introverted percieving, Si and Ni colectively. You'll sometimes also see Pe (extroverted percieving), Ji (introverted judging) and Je (extrovertyed judging). It's a term that gets used quite a lot on this forum, but I'm not sure how far it has spread in the world at large.
What is your personality type?
How do you observe your Pi function when it's pro-active?
How do you observe yourself in general?
How does it feel? What role do feelings have in your Pi?
Additional: Please elaborate with an on function approach
ISTP (I think)
I observe Ni as something I do when there's just nothing else going on. I use it to entertain myself when there's no external stimulation, like when I'm trying to go to sleep.
Not sure how I observe myself in general.
Ni by itself doesn't feel like much of anything to me, but feeling sometimes influences the subject matter.
What do you mean by "an on function approach"? Sorry, I'm sure that's an extremely noobish question.