How can I determine what a shortcut key combination does in Ubuntu 15.10?
Solution 1:
The list of all the keyboard shortcuts and their brief explanation can be accessed through Settings -> Keyboard -> Shortcuts.
Alternatively , the command line way would be
gsettings list-recursively org.gnome.settings-daemon.plugins.media-keys | less
Also you might find useful Ubuntu wiki's Keyboard Shortcuts page
As for what handles the shortcuts , that's gnome-settings daemon (in case of GNOME shell) or unity-settings-daemon (in case of unity). The two are related, keybindings are shared, though not entirely.