SOG is not considered a WDW hotel, so all their restaurants are on a separate system.
Mangino's (Italian) is the only TS restaurant that would take ressies. You would have to call the hotel.
May I suggest you read the reviews on the SOG info thread on this board? You might save yourself time and money if you are considering the Garden Gallery (the buffet).
ETA....I just realized what you were asking. I thought you wanted to know how to make reservations at SOG.