The easiest way is to inspect the "program starter" using the menu editor:
- right-click on the menu button in the taskbar;
Edit Menu - this will open the menu editor.
Now, you can choose the category at the left and the application at the right (
Entries). Just select the application with a single left click, open the context menu with a right-click and select
Properties. A small window will appear, showing (among other information) the command line.
Those program starter files usually reside in
/usr/share/applications, so another approach would be to check the
*.desktop files in that directory. If you're not sure about the name of the
*.desktop to look for, do a grep from inside the
grep gThumb * | grep 'Name='
will give you something like
gthumb.desktop:X-GNOME-FullName=gThumb Image Viewer
gthumb-import.desktop:Name=Import with gThumb
gthumb-import.desktop:X-GNOME-FullName=gThumb Photo Import Tool
Now, you can just use
less gthumb.desktop to inspect the details of that program starter.
Another way would be to use the
apropos command to search a certain keyword in the man pages.