This is the bottom section of the panel. On the left side,
St. Dominic can be identified by his tonsure and habit and by
the dog with the torch beside him.
According to the museum's web page for this painting, the man kneeling on the right "was saved from death when he prayed to the Virgin of the Rosary. Each Hail Mary he recited became a rose that the Christ Child then wove into a garland." The page also says that the pope, emperor, and king behind Dominic "together represent the Christian Estates."
The entire panel
This image in full