meta_query is not allowing to show posts when querying multiple arguments in a WP_Query

Try this one

<?php
$date_today = time();
$args = array(
'post_type' => 'birthday',
'posts_per_page' => 1,
'meta_query' => array(
                      'relation'  =>   'AND',
                      array(
                         'key' => 'field_position',
                         'value' => 'Teacher'
                         ),
                      array(
                          'key' => 'field_dob',
                          'value' => $date_today,
                          'compare' => '=',
                          )

                     )
                    );    

$the_query = new WP_Query($args);


if($the_query->have_posts()) : while($the_query->have_posts()): $the_query->the_post(); 

the_title(); 

endwhile; 

endif; 

?>