One Way:

In SelectedIndex changed event

GridViewRow gvr = GridView1.SelectedRow;

Label lbl = (Label)gvr.Cell[ColumnIndex].Control[0];

Reponse.write(lbl.text);

Second way:

GridViewRow gvr = GridView1.Rows[index];

Label lbl = (Label)gvr.Cells[ColumnIndex].Controls[0];

Reponse.write(lbl.text);

First try to get the row reference in any of the ways & then get the control reference to access it properties.