Question

How does Mr.Beaver know where Edmund has gone? From Lion, The witch and The Wardrobe

Answer 1

Mr. Beaver knew because Lucy mentioned how Edmund had been in Narnia but hadn't known where he'd been. When they started talking about the prophesy Edmund sneaked out of the beaver dome and went to the castle. When the hounds showed up trying to break in Beaver knew he had gone to the The witch's castle.

Answer 2

Mr Beaver was suspicious of Edmund since had been there previously.