org-clock-persist

org-clock-persist is a variable defined in `org-clock.el'.
Its value is

nil

Documentation:
When non-nil, save the running clock when Emacs is closed.
The clock is resumed when Emacs restarts.
When this is t, both the running clock, and the entire clock
history are saved. When this is the symbol `clock', only the
running clock is saved. When this is the symbol `history', only
the clock history is saved.

When Emacs restarts with saved clock information, the file containing
the running clock as well as all files mentioned in the clock history
will be visited.

All this depends on running `org-clock-persistence-insinuate' in your
Emacs initialization file.

You can customize this variable.