The OG contribution is the same that it would have had if you added it to the wort.
Turbinado sugar is contributes pretty much 100% of its weight to the OG thus it adds 46 pppg. The volume is the volume of beer. If you want to be more precise you would include the increase in beer volume when you add the sugar. Each lb of sugar adds about 0.3 qt of volume. But I don’t think that that will make enough of a difference.