social/mail_activity/views/res_partner.xml

<?xml version="1.0" encoding="UTF-8"?>
<odoo>
    <!--
        Copyright 2016 Odoo SA <https://www.odoo.com>
        Copyright 2018 Eficent <http://www.eficent.com>
        License LGPL-3.0 or later (http://www.gnu.org/licenses/lgpl.html).
    -->
    <record id="view_partner_form" model="ir.ui.view">
        <field name="model">res.partner</field>
        <field name="inherit_id" ref="mail.view_emails_partner_info_form" />
        <field name="arch" type="xml">
            <xpath expr="//div[@class='oe_chatter']/field[@name='message_follower_ids']" position="after">
                <field name="activity_ids" widget="mail_activity" />
            </xpath>
        </field>
    </record>
</odoo>