How to get a specific PID #

[rikona]

Running 12.04 updated. I often have several instances of Kate open in
various desktops, and occasionally one of them becomes unresponsive,
but could be closed without losing something important. [Can move
window, no menus come up, no keys seem to do anything, can't close]
How can I find out which PID # is associated with a particular
instance of Kate [or any other pgm] on a particular desktop, so I can
close just THAT instance? I can see them all in htop, but which is
which?

Thanks,

 rikona