You'll have to read your system's man-pages for specifics, I don't have a Solaris system handy. In general you'd

1. Find the PID of the process communicating over loopback which you are interested in. You can use netstat for this, e.g. on Linux
   netstat -nlp --tcp | grep '127\.0\.0\.1'
   will show you all processes listening on the loopback IP for TCP connections.
2. Run truss with the appropriate option to show network system calls with their full argument strings. Using strace (the Linux equivalent to truss) this can be done with
   strace -p <pid> -e trace=network -s 65536