gistfile1.php

<?php

// Add a new field
add_filter( 'job_application_form_fields', 'custom_job_application_form_fields' );

function custom_job_application_form_fields( $fields ) {
  $fields[ 'your_field' ] = array(
    'label'         => 'Label for field',
			'type'        => 'text',
			'required'    => true,
			'placeholder' => 'Placeholder text',
			'priority'    => 6
  );
  $fields[ 'second_field' ] = array(
    'label'         => 'Second for field',
			'type'        => 'text',
			'required'    => true,
			'placeholder' => 'Placeholder text',
			'priority'    => 6
  );
  return $fields;
}

// Add new field data to meta array so its saved and stored
add_filter( 'job_application_form_posted_meta', 'custom_job_application_form_posted_meta' );

function custom_job_application_form_posted_meta( $meta ) {
  $meta['your_field'] = sanitize_text_field( $_POST['your_field'] );
  $meta['second_field'] = sanitize_text_field( $_POST['second_field'] );
  return $meta;
}

// Add a line to the notifcation email with custom field
add_filter( 'create_job_application_notification_message', 'custom_create_job_application_notification_message', 10, 2 );

function custom_create_job_application_notification_message( $message, $application_id ) {
  $message[] = "\n" . "Your field was set as: " . get_post_meta( $application_id, 'your_field', true );  
  $message[] = "\n" . "Your second field was set as: " . get_post_meta( $application_id, 'second_field', true );  
  return $message;
}