Look at the installation instructions:
In the plugin’s root directory you will find a folder called template. You can override that folder and any of the files within, by copying them into your active theme and renaming the folder to /yourtheme/wp_knowledgebase. WP Knowledgebase plugin will automatically load any template files you have in that folder in your theme, and use them instead of its default template files. If no such folder or files exist in your theme, it will use the ones from the plugin.
I would start with copying wp-knowledgebase/template/single-kbe_knowledgebase.php to your theme folder and edit (i.e. add the date) around line 54ff
<h1><?php the_title(); ?></h1>
<?php
the_content();
to something like this
<h1><?php the_title(); ?></h1>
<span class="entry-date"><?php echo get_the_date(); ?></span>
<?php
the_content();
(Untested approach as I haven’t yet done anything apart from installing and activating the plugin)
For hints on how to include the date it might be worth having a look at e.g. your theme’s content-single.php (assuming the post date is shown there)
Additional inspiration for dates is here.
