SARATOGA SPRINGS--When Neil Poznansky, sitting on the back of GI Kentucky Derby and GI Belmont Stakes champion Sovereignty (Into Mischief), saw jockey Junior Alvarado early Friday morning, he wore a wide smile. "How'd I do?" Poznansky said. Alvarado grinned back. No answer necessary. Sovereignty did what Poznansky, Alvarado and Hall of Fame trainer Bill Mott wanted to see as he had his second work since winning the Belmont last month. Working in company with 4-year-old stablemate Jefferson Street (Street Sense), Sovereignty and Poznansky, Mott's assistant, covered four furlongs in :48.99...