how can i fix my display post in my index.php

you’re using commas as concatenators

you’re echoing the_title() and the_post_thumbnail() (use get if you’re
echoing)

your the_post() was at the bottom

<div class="Jobs">
<?php
  if(have_posts()) {
    while (have_posts()) {
      the_post();
      echo'<div class="info_Job">';
      echo '<h2>'.get_the_title().'</h2>';
      echo get_the_post_thumbnail().'</div>'; 
    }
}
?>
</div>

If you don’t want to use get but directly output do this instead:

<div class="Jobs">
<?php
  if(have_posts()) {
    while (have_posts()) {
      the_post();?>
      <div class="info_Job">
        <h2><?php the_title();?></h2>
        <?php the_post_thumbnail();?>
      </div>
<?php }
}
?>
</div>