Doctor Know-all (German: Doktor Allwissend) is a German fairy tale collected by the Brothers Grimm, tale number 98 in Grimm's Fairy Tales. It is Aarne-Thompson type 1641 about being in the right place at the right time. Another tale of this type is Almondseed and Almondella.
A peasant named Crabbe saw how well a doctor ate and asked him how to become one. The doctor told him to buy an ABC book with a rooster up front, sell his oxen and cart to buy doctor's equipment and clothing, and advertise himself as "Doctor Know-all."
Shortly after he set himself up, a nobleman asked him to find stolen money. He insisted on bringing his wife. When they sat to eat, he nudged his wife at each course, saying "That's one," "That's two," and "That's three" — meaning three courses, but the servants bringing in the dishes, the thieves, thought he was identifying them. The fourth one brought in a covered tray of crabs, and the nobleman asked him to guess. Pitying himself, he said, "Poor Crabbe!" and the noble was impressed.
The servants offered to give him the money and a reward as well if he would not betray them. He agreed, and told the nobleman he had to check his book. He was looking for the picture of the rooster and could not find it. He said, "I know you are in there," and the fifth thief servant, hiding in the stove, panicked and fled. He showed the nobleman where the money was, and received a reward from him, too.