SpreadsheetQueryのコンストラクタ引数にシートIDを含んだURLを渡すことで可能です。
string url = "https://spreadsheets.google.com/feeds/spreadsheets/" + sheetId; SpreadsheetQuery query = new SpreadsheetQuery(url); SpreadsheetFeed feed = service.Query(query); SpreadsheetEntry entry = (SpreadsheetEntry)feed.Entries[0]; Console.WriteLine(entry.Title.Text)