Math needed for economic research
Given the level you say you are at I would recommend you to go through this book
Simon and Blume: Mathematics for Economists.
it will give you the core of math skills you need for undergraduate and graduate economics at most universities I would guess. In graduate courses you will probably have to learn more depending on the course and university but it is standard to learn some of the math on the fly when you do economics.
I could recommend other books but they would then be more specialized in certain topics and anyway Simon and Blume is the book that I have most often seen references to on various university courses.
Another virtue of the book is that the examples are to a large extent taken from economics. So you do not &quot;waste your time&quot; on nice mathematical examples that illustrate the mathematical methods but will never appear in economics.
For some graduate courses of course there will be special math skills that are required. Econ departments of some universities specialize in different areas so what you need can also vary from university to university. However, as an economist I would dare say you are very often learning the mathematics as you learn new areas of economics.
Choose a programming language
Although you did not as for a recommendation of this kind, I would strongly encourage you to start programming. Very often being able to simulate some problem in optimization, probability theory, dynamic programming etc. is an invaluable resource to get a deeper understanding of complicated math/economic models.
Currently Matlab is used a lot especially for structural economics. R is very versatile better than Matlab when it comes to econometrics. Python is strong for Machine Learning which is also finding its way into econometrics/economics these days.