Field added by hook_form_alter is not in $node

Nothing personal, but your code is wacked.

Since you are building the form it is not clear why you would even use hook_form_alter().

And ajax callbacks like wc_ajaxtest_t2() can not add form elements (the form function needs to handle that), instead the ajax callback is responsible for returning the change form element(s).

If you want to add a 'field' (note: not part of the Drupal Field API) to a node in hook_form_alter(), you have to do the following:

1) Implement hook_schema() to create a database table to hold your values:

function my_module_schema()
{
  $schema['my_module_field'] = array
  (
    'description' => 'Holds custom form values for my node',
    'fields' => array
    (
      'nid' => array
      (
        'description' => 'The unique Node ID from the {node} table',
        'type' => 'int',
        'unsigned' => TRUE,
        'not null' => TRUE,
      ),
      'value' => array
      (
        'description' => 'The value of the field',
        'type' => 'text',
      ),
    ),
    'primary key' => 'nid',
  );

  return $schema;
}

Note: If you are creating this table after your module is already installed, you will need to implement hook_update_n() with db_create_table() in order to create your database table.

2) Add your field to the node form in hook_form_alter():

function my_module_form_alter(&$form, &$form_state, $form_id)
{
  if($form_id == 'some_node_form')
  {
    $form['my_field'] = array
    (
      '#type' => 'textfield',
      '#title' => t('Enter some text'),
    );
  }
}

3) Save your value in hook_node_insert()

function my_module_node_insert($node)
{
  db_query(
    'INSERT INTO {my_module_field} (nid, value) VALUES (:nid, :value)',
    array(
      ':nid' => $node->nid,
      ':value' => $node->my_field,
    )
  );
}

4) Implement hook_node_update() for the update functionality:

function my_module_node_update($node)
{
  db_query(
    'UPDATE {my_module_field} SET value = :value WHERE nid = :nid',
    array(
      ':value' => $node->my_field,
      ':nid' => $node->nid,
    )
  );
}

5) Load the value in hook_node_load($node)

function my_module_node_load()
{
  if($node->type == 'some_node_type')
  {
    $node->my_field = db_query(
      'SELECT value FROM {my_module_field} WHERE nid = :nid',
      array(
        ':nid' => $node->nid,
      )
    );
  }
}

6) Optionally implement hook_node_view() to display the field when the node is viewed:

function my_module_node_view($node)
{
  if($node->type == 'some_node_type')
  {
    $node->content['my_field'] = array
    (
      '#markup' => check_plain($node->my_field),
      '#prefix' => '<p>',
      '#suffix' => '</p>',
    );
  }
}

With the above process, a database table is created in hook_schema(), the field is added to the node form in hook_node_alter(), the value is saved in hook_node_insert(), the value is updated in hook_node_update(), the value is loaded in hook_node_load() and the value is displayed in hook_node_view().

Note: You would only ever use this process when adding fields to node types that are not created by your module. If you were doing this in the module that created the node type, you would use different hooks.