Get GridView Row and Row Index inside TextChanged event of TextBox inside GridView in ASP.Net

In TextChanged event you can do as following

protected void txtPayAmt_Empty_TextChanged(object sender, EventArgs e)
{
    GridViewRow gvRow = (GridViewRow)(sender as Control).Parent.Parent;
    int index = gvRow.RowIndex;
}

Reference:ASP.Net GridView - Get Row Index on RowCommand and Click events