newsupernova/vendor/magento/module-checkout/etc/fieldset.xml

<?xml version="1.0"?>
<!--
/**
 * Copyright © Magento, Inc. All rights reserved.
 * See COPYING.txt for license details.
 */
-->
<config xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
        xsi:noNamespaceSchemaLocation="urn:magento:framework:DataObject/etc/fieldset.xsd">
    <scope id="global">
        <fieldset id="customer_account">
            <field name="prefix">
                <aspect name="to_order" targetField="customer_prefix" />
            </field>
            <field name="firstname">
                <aspect name="to_order" targetField="customer_firstname" />
            </field>
            <field name="middlename">
                <aspect name="to_order" targetField="customer_middlename" />
            </field>
            <field name="lastname">
                <aspect name="to_order" targetField="customer_lastname" />
            </field>
            <field name="suffix">
                <aspect name="to_order" targetField="customer_suffix" />
            </field>
            <field name="email">
                <aspect name="to_order" targetField="customer_email" />
            </field>
            <field name="group_id">
                <aspect name="to_order" targetField="customer_group_id" />
            </field>
            <field name="tax_class_id">
                <aspect name="to_order" targetField="customer_tax_class_id" />
            </field>
        </fieldset>
        <fieldset id="checkout_onepage_billing">
            <field name="prefix">
                <aspect name="to_customer" />
            </field>
            <field name="firstname">
                <aspect name="to_customer" />
            </field>
            <field name="middlename">
                <aspect name="to_customer" />
            </field>
            <field name="lastname">
                <aspect name="to_customer" />
            </field>
            <field name="suffix">
                <aspect name="to_customer" />
            </field>
            <field name="email">
                <aspect name="to_customer" />
            </field>
            <field name="customer_dob">
                <aspect name="to_customer" targetField="dob" />
            </field>
            <field name="customer_taxvat">
                <aspect name="to_customer" targetField="taxvat" />
            </field>
            <field name="customer_gender">
                <aspect name="to_customer" targetField="gender" />
            </field>
        </fieldset>
        <fieldset id="checkout_onepage_quote">
            <field name="customer_prefix">
                <aspect name="to_customer" targetField="prefix" />
            </field>
            <field name="customer_firstname">
                <aspect name="to_customer" targetField="firstname" />
            </field>
            <field name="customer_middlename">
                <aspect name="to_customer" targetField="middlename" />
            </field>
            <field name="customer_lastname">
                <aspect name="to_customer" targetField="lastname" />
            </field>
            <field name="customer_suffix">
                <aspect name="to_customer" targetField="suffix" />
            </field>
            <field name="customer_email">
                <aspect name="to_customer" targetField="email" />
            </field>
            <field name="customer_dob">
                <aspect name="to_customer" targetField="dob" />
            </field>
            <field name="customer_taxvat">
                <aspect name="to_customer" targetField="taxvat" />
            </field>
            <field name="customer_gender">
                <aspect name="to_customer" targetField="gender" />
            </field>
        </fieldset>
    </scope>
</config>