Get a list of Terms for a specific category

The following code will do it. Please change the ‘filter’ text in the below code to whatever filters taxonomy name you have set.

if(is_category() ){

    $thiscat = get_queried_object_id(); 
    $filter_tax = array();
    $args = array( 'category' => $thiscat );
    $lastposts = get_posts( $args );

    foreach ( $lastposts as $post ){
        setup_postdata( $post );
        $terms = get_the_terms( $post->ID, 'filter' ); // Change the taxonomy name here

        if ( $terms && ! is_wp_error( $terms ) ){

         foreach ( $terms as $term ) {
            $filter_tax[] = $term;
         }

        }
    }
    wp_reset_postdata();

    if( !empty($filter_tax) ){
        print_r($filter_tax);
    } else {
        echo 'No filter set.';
    }

}