Call web service via Ajax with focusout function

 $("#<%=txtProduto.ClientID%>").on("focusout", function (event) {
            event.preventDefault();
            $.post(AjaxService.Pessoa(<%=txtProduto.ClientID%>), function (data) {
                $("#<%=txtPrecoUnitario.ClientID%>").val(data);
            });

        });

I'm trying to call web service service via Ajax , and this has parameters and should return me a value too.

The code above was what I tried but did not work.