Add this to your child theme’s functions.php file:

add_action('under-comic-top', 'mytheme_add_jetpack_share_buttons');

function mytheme_add_jetpack_share_buttons() {
	global $post;
	if (function_exists('sharing_display')) {
		$switched_status = get_post_meta( $post->ID, 'sharing_disabled', false );
		if (empty( $switched_status )) echo sharing_display();
	}
}

and the CSS overrides for it inside your child themes style.css

div.sharedaddy .sd-content {
	margin: 0 auto !important;
	width: 300px !important; /* change this width based on which buttons and styles you are using */
	float: none !important;
}

Make sure you have it enabled in Jetpack and you have chosen which services to use as sharing buttons and their style.

– Phil