Using bootstrap’s modal you could use this hook in your function.php file top do that:
add_filter( 'nav_menu_link_attributes', 'menu_atts', 10, 3 );
function menu_atts( $atts, $item, $args )
{
// The ID of the target menu item
$menu_target = 24;
// inspect $item
if ($item->ID == $menu_target) {
$atts['data-toggle'] = 'modal';
$atts['data-target'] = '#IDofModal';
}
return $atts;
}