Directly related to knowledge:
* A walking, talking library: This is the most direct translation.
* A repository of knowledge: This emphasizes the vastness of their information.
* A human encyclopedia: This is a literal interpretation, emphasizing their ability to access information readily.
More figurative options:
* A fount of information: This suggests that the person is a constant source of knowledge.
* A mine of information: This implies that the person has an abundance of knowledge, like a mine has resources.
* A walking, talking dictionary: This highlights the precise nature of their knowledge.
Humorous options:
* A knowledge sponge: This implies that the person absorbs information easily.
* A human Google: This plays on the prevalence of online search engines.
The best idiom to use will depend on the context and the tone you want to convey.