Hi Steve,
There is no standard way to do so.
One way to achieve this is to query the database and check all the parent processes. But this is quite cumbersome.
So as a quick tweak, you can do below to achieve this:
The subprocess you have modified might have some variable mappings with parent process. So you can change one of the mapped variable type in subprocess. Then all the process which are calling this subprocess will show validation error in 'Validation Report'. This way you can come to know what all processes are calling that particular sub-process.
Basically the idea is to find out a common reference; change it so that parent shows error; This way you can get the list of processes.
Regards,
Varun Nohria