you can use like this
protected void Page_Init(object sender, EventArgs e)
{
try
{
DropDownList ddlParent =(DropDownList)Master.FindControl("ddlParent");
if (ddlParent != null)
{
ddlParent .SelectedIndexChanged += new EventHandler(lnkReferesh_Click);
}
}
catch (Exception ex)
{
throw ex;
}
}
[Edit]:Set proper code block.