Use the GroupFromPoint property to get the group from the point specified by the {X,Y}. The X and Y coordinates are expressed in client coordinates, so a conversion must be done in case your coordinates are relative to the screen or to other window. If the X parameter is -1 and Y parameter is -1 the GroupFromPoint property determines the group from the cursor. Use the ItemFromPoint property to get the cell or item from the cursor. Use the ColumnFromPoint property to access the column over the point. Use the GroupFromPoint property to get the group's caption from the cursor. Use the GroupListFromPoint property to get the group's list from cursor. 

The following VB sample displays the group's caption from the cursor:

Private Sub ExplorerTree1_MouseMove(Button As Integer, Shift As Integer, X As Single, Y As Single)
    Dim g As EXPLORERTREELibCtl.Group
    With ExplorerTree1
        Set g = .GroupListFromPoint(X / Screen.TwipsPerPixelX, Y / Screen.TwipsPerPixelY)
        If Not (g Is Nothing) Then
            Debug.Print g.Caption
        End If
    End With
End Sub

The following VFP sample displays the group's caption from the cursor:

with thisform.Olecontrol1
	local g
	g = .GroupFromPoint(-1,-1)
    If !isnull(g) Then
    	with g
			wait window .Caption nowait
	    endwith
    EndIf
endwith