1)
Code:
$ gsettings list-keys org.gnome.shell.clock
2) You will see on the terminal:
Code:
show-date
show-seconds
3) Since the clock already shows the day of the week and the time, we're only interested in adding the date to the clock:
Code:
$ gsettings set org.gnome.shell.clock show-date true
Note that these commands will show errors if you run them as root.