ahhhh!
Actually your code should work but you need to change it to this:
<?php
$selected = get_field('q_and_a_category_select');
$args=array(
'post_type' => 'q-and-a',
'q_and_a_category' => "$selected" //the slug for the custom taxonomy term
);
$my_query = new WP_Query($args);
if( $my_query->have_posts() ) {
while ($my_query->have_posts()) : $my_query->the_post(); ?>
<?php the_title(); ?>
<?php endwhile; }?>
<?php wp_reset_query(); ?>
you could put the get_field directly in the array but I think this looks more structured 🙂
