Could not find template
This is index.php in the current active theme, you should always create custom templates in the template folder in your theme.
The most simple way to create a template for the current post is to create one of the following files:
Twig
- template/post/default.twig
- template/post/zo-doen-we-het.twig
- template/post/2446.twig
PHP
- template/post/default.php
- template/post/zo-doen-we-het.php
- template/post/2446.php
The requested post was Zo doen we het! (basisregels RSG) which has ID 2446.