how to get views field names/values for hook_views_pre_render?
How do I get the available values to work with?  


To get values from result you can do something like:
$value-&gt;_entity-&gt;title-&gt;getValue()[0]['value'];
Here is example to get body and title you can do the same with other fields.

/**
 * Implements hook_views_pre_render().
 */
function mymodule_views_pre_render(ViewExecutable $view) {
  if ($view-&gt;id() == 'viewname' &amp;&amp; $view-&gt;current_display == 'page_1') {
    foreach ($view-&gt;result as $key =&gt; $value) {
      //- Get title value 
      $title_value =  $value-&gt;_entity-&gt;title-&gt;getValue()[0]['value'];
      //- Get body value
      $body_value =  $value-&gt;_entity-&gt;body-&gt;getValue()[0]['value'];
     //- Get Other field values ...
    }
  }
}