The tool tip text is handled in the ToolTipTextNeeded event handler. In our application, we needed the tool tip in RadGridView2, only when hovering over the 1st column (0). To simplify things, we returned the tool tip text in the query that populated the grid and stored the text in a non-visible column (6). Here is the completed code:
Private Sub RadGridView2_ToolTipTextNeeded(sender As Object, e As ToolTipTextNeededEventArgs) Handles RadGridView2.ToolTipTextNeeded
Dim o As GridDataCellElement = TryCast(sender, GridDataCellElement)
If o.ColumnIndex = 0 Then
e.ToolTipText = "Order: " + RadGridView2.CurrentRow.Cells(6).Value.ToString
End If
End Sub
Substitute your text for the e.ToolTipText line.