shadow-todo-file

shadow-todo-file is a variable defined in `shadowfile.el'.
Its value is

nil

Documentation:
File to store the list of uncopied shadows in.
This means that if a remote system is down, or for any reason you cannot or
decide not to copy your shadow files at the end of one Emacs session, it will
remember and ask you again in your next Emacs session.
This file must NOT be shadowed to any other system, it is host-specific.
Default: ~/.emacs.d/shadow_todo

You can customize this variable.