Would depend on the platform you're running on...

In Unix, I believe it's

ps -ef | grep 'foo.exe'

ps is the unix command to list processes currently running. The switch -ef shows extended information for all processes currently running for all users. If the program is running under your username, then just use ps with no options and you'll have less to sort through.

This is assuming the process is still running in the background and you have access to a command prompt.