Hard to answer without knowledge of prior background or exposure that you might have.
As a rule of thumb, I would advise to start with elementary linear algebra, statistics, and probability. Edit: As pointed out by a reply comment, these require a good grasp of calculus.
Notation is only syntactic, most importantly you want to understand the semantics (i.e the significance of the construction your are studying). To achieve this, you need to do the proper background work and the rest will follow naturally.
This. I mean you can google stuff like "what does the curly L mean" and it would tell you that it's a Lie derivative, but that wouldn't mean much to you unless you understood that it did.
So you need to understand the work and the math behind it and you will get an idea about the notations used. Not the other way round.
As a rule of thumb, I would advise to start with elementary linear algebra, statistics, and probability. Edit: As pointed out by a reply comment, these require a good grasp of calculus.
Notation is only syntactic, most importantly you want to understand the semantics (i.e the significance of the construction your are studying). To achieve this, you need to do the proper background work and the rest will follow naturally.