Javascript in Drupal
Do I need to indicate where is my js file?

Of course, js files do not auto magically get loaded.
You need to tell Drupal about them, There are various ways, see Adding JavaScript to your theme or module.
function draws_form_alter(&amp;$form, &amp;$form_state, $form_id) {
  switch($form_id) {
    case 'bets_node_form':
      $form['field_possible_returns']['und'][0]['value']['#process'] = array('my_custom_process');
      // Load JS File
      $form['#attached']['js'] = [
         drupal_get_path('module', 'draws') . '/draws.js',
      ];
      break;
  }
}