How to display field “VAT Number” (required) during registration.
This field is visible when editing the user from the administration panel. Only how to display them during registration? 
I found code in:
app/design/frontend/{YOUR_PACKAGE}/{YOUR_THEME}/Magento_Customer/templates/form/register.phtml This file contains fields that are displayed during registration:
<input type="hidden" name="create_address" value="1" /> <div class="field company"> <label for="company" class="label"><span><?php /* @escapeNotVerified */ echo __('Company') ?></span></label> <div class="control"> <input type="text" name="company" id="company" value="<?php echo $ block->escapeHtml($ block->getFormData()->getCompany()) ?>" title="<?php /* @escapeNotVerified */ echo __('Company') ?>" class="input-text <?php /* @escapeNotVerified */ echo $ this->helper('Magento\Customer\Helper\Address')->getAttributeValidationClass('company') ?>"> </div> </div> <div class="field telephone"> <label for="telephone" class="label"><span><?php /* @escapeNotVerified */ echo __('Phone Number') ?></span></label> <div class="control"> <input type="text" name="telephone" id="telephone" value="<?php echo $ block->escapeHtml($ block->getFormData()->getTelephone()) ?>" title="<?php /* @escapeNotVerified */ echo __('Phone Number') ?>" class="input-text <?php /* @escapeNotVerified */ echo $ this->helper('Magento\Customer\Helper\Address')->getAttributeValidationClass('telephone') ?>"> </div> </div> <?php $ _streetValidationClass = $ this->helper('Magento\Customer\Helper\Address')->getAttributeValidationClass('street'); ?> <div class="field street required"> <label for="street_1" class="label"><span><?php /* @escapeNotVerified */ echo __('Street Address') ?></span></label> <div class="control"> <input type="text" name="street[]" value="<?php echo $ block->escapeHtml($ block->getFormData()->getStreet(0)) ?>" title="<?php /* @escapeNotVerified */ echo __('Street Address') ?>" id="street_1" class="input-text <?php /* @escapeNotVerified */ echo $ _streetValidationClass ?>"> <div class="nested"> <?php $ _streetValidationClass = trim(str_replace('required-entry', '', $ _streetValidationClass)); ?> <?php for ($ _i = 2, $ _n = $ this->helper('Magento\Customer\Helper\Address')->getStreetLines(); $ _i <= $ _n; $ _i++): ?> <div class="field additional"> <label class="label" for="street_<?php /* @escapeNotVerified */ echo $ _i ?>"> <span><?php /* @escapeNotVerified */ echo __('Address') ?></span> </label> <div class="control"> <input type="text" name="street[]" value="<?php echo $ block->escapeHtml($ block->getFormData()->getStreetLine($ _i - 1)) ?>" title="<?php /* @escapeNotVerified */ echo __('Street Address %1', $ _i) ?>" id="street_<?php /* @escapeNotVerified */ echo $ _i ?>" class="input-text <?php /* @escapeNotVerified */ echo $ _streetValidationClass ?>"> </div> </div> <?php endfor; ?> </div> </div> </div> <div class="field required"> <label for="city" class="label"><span><?php /* @escapeNotVerified */ echo __('City') ?></span></label> <div class="control"> <input type="text" name="city" value="<?php echo $ block->escapeHtml($ block->getFormData()->getCity()) ?>" title="<?php /* @escapeNotVerified */ echo __('City') ?>" class="input-text <?php /* @escapeNotVerified */ echo $ this->helper('Magento\Customer\Helper\Address')->getAttributeValidationClass('city') ?>" id="city"> </div> </div> <div class="field region required"> <label for="region_id" class="label"><span><?php /* @escapeNotVerified */ echo __('State/Province') ?></span></label> <div class="control"> <select id="region_id" name="region_id" title="<?php /* @escapeNotVerified */ echo __('State/Province') ?>" class="validate-select" style="display:none;"> <option value=""><?php /* @escapeNotVerified */ echo __('Please select a region, state or province.') ?></option> </select> <input type="text" id="region" name="region" value="<?php echo $ block->escapeHtml($ block->getRegion()) ?>" title="<?php /* @escapeNotVerified */ echo __('State/Province') ?>" class="input-text <?php /* @escapeNotVerified */ echo $ this->helper('Magento\Customer\Helper\Address')->getAttributeValidationClass('region') ?>" style="display:none;"> </div> </div> <div class="field zip required"> <label for="zip" class="label"><span><?php /* @escapeNotVerified */ echo __('Zip/Postal Code') ?></span></label> <div class="control"> <input type="text" name="postcode" value="<?php echo $ block->escapeHtml($ block->getFormData()->getPostcode()) ?>" title="<?php /* @escapeNotVerified */ echo __('Zip/Postal Code') ?>" id="zip" class="input-text validate-zip-international <?php /* @escapeNotVerified */ echo $ this->helper('Magento\Customer\Helper\Address')->getAttributeValidationClass('postcode') ?>"> </div> </div> <div class="field country required"> <label for="country" class="label"><span><?php /* @escapeNotVerified */ echo __('Country') ?></span></label> <div class="control"> <?php echo $ block->getCountryHtmlSelect() ?> </div> </div> <?php $ addressAttributes = $ block->getChildBlock('customer_form_address_user_attributes');?> <?php if ($ addressAttributes): ?> <?php $ addressAttributes->setEntityType('customer_address'); ?> <?php $ addressAttributes->setFieldIdFormat('address:%1$ s')->setFieldNameFormat('address[%1$ s]');?> <?php $ block->restoreSessionData($ addressAttributes->getMetadataForm(), 'address');?> <?php echo $ addressAttributes->setShowContainer(false)->toHtml()?> <?php endif;?> <input type="hidden" name="default_billing" value="1"> <input type="hidden" name="default_shipping" value="1"> </fieldset> I also found this code in this file:
<?php $ _taxvat = $ block->getLayout()->createBlock('Magento\Customer\Block\Widget\Taxvat') ?> <?php if ($ _taxvat->isEnabled()): ?> <?php echo $ _taxvat->setTaxvat($ block->getFormData()->getTaxvat())->toHtml() ?> <<?php endif ?> 
