shortcode-get-single-post-cat.php

<?php

/**
 * Get Post Category
 * 
 * Shortcode: [post_category]
 */
function shortcode_post_category($atts=array()) {
	// get taxonomy by post type
	$tax = get_object_taxonomies(get_post_type());

	// get the categories of the taxonomy
	$cats = get_the_terms($post->ID, $tax[0]);

	$result = '';
	foreach ($cats as $cat) {
		$result = $cat->name;
		return $result;
	}
	return $result;
}
add_shortcode('post_category', 'shortcode_post_category');