board_id 등 값은 적절히 수정해주세요.

<?php
global $wpdb;
echo $wpdb->get_var("SELECT COUNT(*) FROM `{$wpdb->prefix}kboard_board_content` WHERE `board_id`='1' AND `category1`='카테고리1'");
?>

<?php
global $wpdb;
echo $wpdb->get_var("SELECT COUNT(*) FROM `{$wpdb->prefix}kboard_board_content` WHERE `board_id`='1' AND `category2`='카테고리2'");
?>