Use the lsof command to see what processes are using what files. You can also use the fuser command but lsof is more general. If you wanted to see what processes are using what files on the root partition then the following command would do the trick.
Then you can use the ps command with the ASCII forest output format to see the parent process of the child running whatever command you are interested in diagnosing.
If you can't see the ends of the lines then use the --width parameter to tell ps that you are using a 132 column terminal. That will cause ps to write the entire line and wrap the output.