Progress:

In an lxterminal either as knoppix or root,
ctl-alt-F2 gets a virtual terminal (I don't know which one).
alt-F12 then takes you to virtual terminal #12 (vt #12).
vt #12 displays the last 46 lines of the grey-on-black diary.
From vt #12, alt-F5 then takes you back to your X-session.

Note: The previous is true in my Knoppix 6.2.1, with my
Inspiron 1545 keyboard, but not in Ubuntu 10.04 on another
computer.

Musings:

I am guessing that the diary which may have existed on prior
screens probably went to /dev/null, and isn't retrievable.

I don't know how to pre-arrange for an lxterm to be active
to see this stuff from the get-go.

I suspect a well-placed tee command might capture this
lost material in a logfile for later viewing.