TV highlights: D.C. restaurateur Mike Isabella is challenged on 'Top Chef Duels'

The top six finalists team with all-stars to perform on "So You Think You Can Dance" (Fox at 8 p.m.), with Christina Applegate playing guest judge and a performance from Rixton. "Who Do You Think You Are?" (TLC at 9) welcomes Kelsey Grammer and unearths a dark past complete with demons and a great migration.