It's hard to recommend one thing, there's a whole stack of knowledge that this stuff is based on, and it depends what you're already comfortable with. For example if you wanted to learn STARKs (as I do, but haven't yet), there's a whole different bunch of mathematical machinery compared with SNARKs or Bulletproofs. This uses the latter. You could do worse than read my old doc that slowly builds up the concepts behind bulletproofs, including what 'ZK' means: https://github.com/AdamISZ/from0k2bp . You can look for detailed books that cover all the preliminaries like the "moonmath manual" (search it), or shorter more conceptual things like Matthew Green's cryptography blog that has iirc a 3 part intro to ZKPs. You can find much more rigorous academic stuff like the Crypto Book of Boneh and Shoup which gives pieces of the picture but isn't yet completed. You can read Vitalik Buterin's old blog posts explaining zkSNARKs from the ground up (he's always been a really good technical writer, one of the best actually). And at the end of the day, the academic papers will really help too. If you need more general cryptography knowledge, different recommendations would apply :)

Btw on bulletproofs specifically look up the dalek cryptography blogs/docs, they are the best in terms of details, diagrams. 

 This is sick 🙏 

 Thank you very much for the thoughtful reply. Had a feeling it was rather spread out, so this will help point me in the right direction. Wish me luck 

 Was gonna zap you, but can’t seem to find the usual icon on profile :(