You can't get the full file path of the client side original file path. but you can get the file name as below
fileNameTxt.Text =fileupload.FileName;
if you need to display the content of the file in a text box;
protected void btnUpoad_ServerClick(object sender, EventArgs e)
{
if(fileupload1.HasFile)
{
fileNameTxt.Text =fileupload.FileName.ToString();
fuUpload.SaveAs(Server.MapPath("images")+"\\"+fileupload1.FileName);
fileContent.Text =File.ReadAllText(Server.MapPath("images")+"\\"+fileupload1.FileName);
}
}