How do I know if a process is waiting on another process and get that processes pid

["Grizzly(Francis Smit)" <grizzly smit id au>]

yep that sums it up I have a vte_terminal inside it I have a shell 
running if the shell should be waiting on a child process say sudo su - 
to terminate how can I detect this and how can I get the child's pid

all this is on linux so I don't care about portability just now