$(document).on("click", ".btnInsere", function () {

    var _id = $('#divSP').find('input[name=txtValor]').data('valor');

    });

<div id="divSP">
<table id="tblPrincipal"
<thead>
    <th>
        <td></td>
        <td></td>
    </th>
</thead>
<tbody>
    <tr>
        <td>
            <!--Table 1-->
            <table>
            <thead>
                <th>
                    <td> </td>
                    <td></td>
                </th>
            </thead>
            <tbody>
                <tr>
                    <td><input type="text" class="txtValor" name="txtValor[]" id="@item.valor" data-valor="@item.valor" value="Arroz"/> </td>
                    <td><input type="button" class="btnInsere" name="btnInsere" id="btnInsere" value="Insere"/></td>
                </tr>
            </tbody>
            </table>
    </tr>
    <tr>
            <!--Table 2-->
            <table>
            <thead>
                <th>
                    <td> </td>
                    <td></td>
                </th>
            </thead>
            <tbody>
                <tr>
                    <td><input type="text" class="txtValor" name="txtValor[]" id="@item.valor" data-valor="@item.valor" value="Feijão"/> </td>
                    <td><input type="button" name="btnInsere" id="btnInsere" value="Insere"/></td>
                </tr>
            </tbody>
            </table>
    </tr>
    <tr>
            <!--Table n... -->
            <table>
            <thead>
                <th>
                    <td> </td>
                    <td></td>
                </th>
            </thead>
            <tbody>
                <tr>
                    <td><input type="text" class="txtValor" name="txtValor[]" id="@item.valor" data-valor="@item.valor" value="Salada"/> </td>
                    <td><input type="button" name="btnInsere" id="btnInsere" value="Insere"/></td>
                </tr>
            </tbody>
            </table>
        </td>

    </tr>
</tbody>
</table>
</div>