Ori
I can look at this back at my desktop. As I understand tiddlywiki does not currently track this. Rather it tracks tiddlers opened and focused on such as edited, in the historylist. As a result until you navigate to a new tiddler the last closed may be what you want. Also by displaying the history it is posible to see where you have being which is more functionality than your request.
I will share that shortly.
It is posible to add additional actions to the close button to record the tiddler title thus providing access to the last closed. I just started something similar for edit and done buttons.