'Book of Changes' is the English translation for the Chinese 'I Ching', a millennium book about mysticism, wisdom and religion written so-so in the 4th century BC. It is one of the most important books in all history and it is used now-a-days still.
Melinda calls the hot dog cart where her and Eli get lunch The Umbrella Room. This is a callback to the season 2 episode "The Night Wet Met," where Jim takes Melinda to a hot dog cart for their first date and calls it The Umbrella Room.