According to
http://www.rockbox.org/wiki/CustomWPS#File_Info%d(1) First directory from end of file path.
But it doesn't show up.
[If I replace the line with %fn (File Name) or any other tag, it does]
Edit
I have made it
Here's a piece of code with it and more:
# Track Info Viewport:
%V(0,14,-,38,1)
# FILE NAME
%ac%fn
# CLOCK
%ac%?St(time format)<%cH|%cl>:%cM
# FOLDER
%ac%?d(1)<%d(1)|%(root%)>