A.Your best option would be to insert Label CKLbl = e.Item.FindControl("lblQty") as Label at line4.
B.Your best option would be to insert Label CKLbl = Page.FindControl("lblQty") as Label at line 4.
C.Your best option would be to insert Label CKLbl = rptData.FindControl("lblQty") as Label at line4.
D.Your best option would be to insert Label CKLbl = e.Item.Parent.FindControl("lblQty") as Labelat line 4