contract/agreement/views/res_partner.xml

<?xml version="1.0"?>
<odoo>

    <record model="ir.ui.view" id="partner_form">
        <field name="model">res.partner</field>
        <field name="inherit_id" ref="base.view_partner_form"/>
        <field name="arch" type="xml">
            <xpath expr="//page[@name='internal_notes']" position="after">
                <page name="agreement" string="Agreements">
                    <group colspan="2" col="2">
                        <field name="agreements_ids" string="Agreements" />
                    </group>
                </page>
            </xpath>
        </field>
    </record>
</odoo>