I want to add a sub menu to the top of the wiki pages,

I want to add a sub menu to the top of the wiki pages, and am trying to do it using <?php wp_nav_menu( array('menu' => 'Wiki' )); ?>
although i am not sure if that is right at all, or precisely which file to add it in.

Is it possible to include a sub menu in the wiki template, and how does one go about doing this

thanks