A person who knows a lot can be described using several terms, depending on the context:

• Expert : Someone with extensive knowledge or skill in a particular area.
• Scholar : A person who has studied a subject deeply, often in an academic setting.
• Savant : A person with profound knowledge, sometimes in a specific field.
• Polymath : Someone who knows a lot about many different subjects.
• Intellectual : A person who engages in critical thinking and has a broad knowledge base.
• Wise person : Someone who has gained knowledge through experience and good judgment.

If you want a single word or a more specific term, let me know!