The shrewdest person is very clever and good at understanding things.
Being shrewd is usually a good thing, but it can also mean someone is tricky or not completely honest.
Examples:
She is the shrewdest person I know.
The shrewdest fox always gets the most food.
The shrewdest students always get the best grades.
The shrewdest cat always catches the most mice.
The shrewdest detective always solves the hardest cases.
He is the shrewdest businessman in town.