Community Tip - Did you get an answer that solved your problem? Please mark it as an Accepted Solution so others with the same problem can find the answer easily.
X
Session ID is the ID number that Pro|E assigns to every part or assy opened. The numbers are assigned as things are opened and change with every session of Pro|E. I don't think you can show them in the model tree, but you can find them while in an assy be going to relations, then show -> session ID.