org-log-note-clock-out

org-log-note-clock-out is a variable defined in `org.el'.
Its value is

nil

Documentation:
Non-nil means record a note when clocking out of an item.
This can also be configured on a per-file basis by adding one of
the following lines anywhere in the buffer:

#+STARTUP: lognoteclock-out
#+STARTUP: nolognoteclock-out

You can customize this variable.