• launch-prefix="xterm -e gdb --args": run your node in a gdb in a separate xterm window, manually type run to start it
• launch-prefix="gdb -ex run --args": run your node in gdb in the same xterm as your launch without having to type run to start it
If you already tried the two launch-prefixes I list above, but still can't find the window, make sure it is not being spawned behind the terminal you use to roslaunch everything in. That has happened to me some times and it can make for a confusing 5 minutes.