1. [POST & CATEGORY] get_the_category() để xem bài viết thuộc category nào (lấy chi tiết category)

https://developer.wordpress.org/reference/functions/get_the_category/

get_the_category( int $post_id = false )

$post_id
(int) (Optional) The post ID. Defaults to current post ID.

Default value: false

C:\xampp\htdocs\wordpress\wp-content\themes\twentytwentyone\header.php

<?php  
	$categories = get_the_category();
	echo '<pre>';
		var_export($categories);
	echo '</pre>';
?>