Vicky Jo (Icky Vicky had a squeaky ball) has a neat distinction between Ps and Js. She asks you to do two arm motions. One of them will feel more comfortable than the other, and this should tell you whether you are a P or a J. It's a very simple dichotomy and you can't go wrong with it. Try it and report your preference and whether it makes sense, please. I came out clearly as a P so changed my distinction from J to P.
http://www.infjorinfp.com/docs/PreferredCommunicationStyle.htm
http://www.infjorinfp.com/docs/PreferredCommunicationStyle.htm