The wisest or most knowledgeable.
Being sagest is a very good thing. It means you know a lot and can help others.
Examples:
The old man is the sagest person I know.
She gave me the sagest advice.
The sagest people are often good listeners.
The cat looked at me with its sagest face.
He is the sagest person in the whole world!
The sagest owl in the forest helped the other animals.