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.';
}
}