Take a look at the Action that is attached to the Menu Item. (If you access this from the Edit Action option in the Debug menu (Developer Mode) it is easier to find.)

It defaults to type tree_account_move_line_quickadd

Then, you find account_move_line_quickadd.xml exists in \addons\account\static\src\xml\

<t t-name="AccountMoveLineQuickAdd">
    <div class="oe_account_quickadd ui-toolbar" style="margin-bottom:0px;">
        <div class="oe_form_dropdown_section">
            <h4>Period :</h4> 
            <select class="oe_account_select_period">

            </select>
        </div>
        <div class="oe_form_dropdown_section">
            <h4>Journal :</h4> 
            <select class="oe_account_select_journal" >

            </select>
        </div>
    </div>
</t>