The graph dialog is part of the scene object properties dialog, which is located at [Menu bar --> Tools --> Scene object properties]. You can also open the dialog with a double-click on an object icon in the scene hierarchy, or with a click on its toolbar button:
[Scene object properties toolbar button]
In the scene object properties dialog, click the Graph button to display the graph dialog (the Graph button only appears if the last selection is a graph). The dialog displays the settings and parameters of the last selected graph:
The graph object itself is mainly operated via a customization script, that could be adapted in various ways, if needed. The behaviour of the graph can also be altered in various ways by clicking the user parameter icon next to the customization script.