sidebar missing on category pages (twenty eleven theme)

Hi @ibrahima,

Thanks for posting on the forum.

To display the sidebar on category pages on twenty eleven theme create a page template file page.php in your child theme and add the following code in it.

<?php
/**
 * Template for displaying all pages
 *
 * This is the template that displays all pages by default.
 * Please note that this is the WordPress construct of pages
 * and that other 'pages' on your WordPress site will use a
 * different template.
 *
 * @package WordPress
 * @subpackage Twenty_Eleven
 * @since Twenty Eleven 1.0
 */

get_header(); ?>

		<div id="primary">
			<div id="content" role="main">

				<?php while ( have_posts() ) : the_post(); ?>

					<?php get_template_part( 'content', 'page' ); ?>

					<?php comments_template( '', true ); ?>

				<?php endwhile; // end of the loop. ?>

			</div><!-- #content -->
		</div><!-- #primary -->
<?php  if ( get_post_type() == 'product') { get_sidebar(); } ?>
<?php get_footer(); ?>

Also add the following CSS code in the style.css file of your child theme or add it in your site using the following plugin.

http://wordpress.org/plugins/simple-custom-css

body.tax-product_category.singular #primary {
	margin: 0 -26.4% 0 0;
}
body.tax-product_category.singular #content{
	margin: 0 34% 0 7.6%;
	width: 58.4%;
}

Best Regards,
Vinod Dalvi