What math topics are most needed to become data scientist?
Linear Algebra, Calculus, Probability and Statistics are fundamental topics.

Lots of great books out there, Khan Academy is a good resource as well:

https://www.khanacademy.org/math/linear-algebra

https://www.khanacademy.org/math/calculus-1

https://www.khanacademy.org/math/statistics-probability