Where to insert .js code using the webform module for google tracking a submit button?
you have 2 option:
1- using #attached to the $form element. use hook_form_alter

function YourMODULE_form_webform_client_form_1_alter(&amp;$form, &amp;$form_state) {
  $form['#attached']['js'] = array(
    drupal_get_path('module', 'YourMODULE') . '/js/your_script.js',
  );
}


2- add it in your custom module with drupal_add_js() function, Also it will be much better if you just load the js on only that page (web form page) so you will avoid loading it on every page.