В вашей форме есть такие поля:
echo $this->Form->input('direccion');
echo $this->Form->input('persona.nombre');
echo $this->Form->input('persona.voluntario.cv');
В контроллере Volunteer есть такой код:
if ($this->request->is(['patch', 'post', 'put'])) {
$contact_table = TableRegistry::get('Contactos');
$contact = $contact_table->patchEntity($contact, $this->request->data, [
'associated' => ['Personas' => ['Voluntarios']]
]);
if ($contact_table->save($contact)) {
// etc.