I usually save the session with the graphical app xfce4-session-settings (Session -> Save Session). Can this be also done from the command-line? How?
@guest123 pointed to this page. To sum it up, you have to run this:
$ dbus-send --session --dest=org.xfce.SessionManager --print-reply \ /org/xfce/SessionManager org.xfce.Session.Manager.Checkpoint string:""
It works for me with Xfce 4.12.