This is what worked for me in Mavericks 10.9.1. I had just migrated to a new Mac.
With a Finder window open, go to View > Show View Options and make sure "Show Library Folder" is checked on.
Now open User > Library and you should see the folder ToDoLists (don't do anything with it). If you don't see it then something has gone wrong.
Launch the To-do-Lists app and from the menu go to File > Open Backup and browse to User > Library > ToDoLIsts > ToDoListsDatabase.tdl
That should load all your to lists back in.