I have found a solution

The error was because Gave different field inside template than on the outside now my code is:

<record id="projection_view_kanban" model="ir.ui.view">
    <field name="name">projection.target.kanban</field>
            <field name="model">projection.target</field>
    <field name="priority" eval="8"/>
    <field name="arch" type="xml">
        <kanban class="o_res_partner_kanban" create="false">
            <field name="sales_man"/>
            <field name="target" />
            <field name="sal" />
        <templates>
            <t t-name="kanban-box">
                <div class="oe_kanban_global_click o_res_partner_kanban" style="background-color:#00438a;color:#fff;border-radius:15px;">
                <div class="oe_kanban_details">
                <strong class="o_kanban_record_title oe_partner_heading" style="font-size:16px;">
                    <field name="sales_man" style="display:block;"/>
                </strong>
                    <span style="display:block;">Target:<field name="target" /></span>
                    <span style="display:block;">Achievement:<field name="sal" /></span>
                </div>
                </div>
            </t>
        </templates>
        </kanban>
    </field>
</record>