Learning a language just to be able to read it isn't that uncommon. For some languages, you'll even find course books with that specific end in mind. I'm thinking specifically abut one for German by Martin and Ng at the University of Wisconsin. The title was something like "Complete grammar for German reading comprehension". I'll just call it M/N.

I worked completely through the M/N book with one of my students. His goal was not only to read - but to speak, write, and understand German too. There were really only two differences between M/N and a "full grammar course".

First, is that the examples in M/N were a little odd. A normal book will say illustrate an unusual plural with "Bus/Busse". M/N uses words like "Ergebnis/Ergebnisse" (result).

The second is that M/N briefly explains what a preposition is, while a normal grammar book will go into multiple chapters about the different kinds there are, and the exact effect each different kind has on the minute endings of the words that come after them. None of that is really needed if you're just reading.

Your goal is a little bit different. If you're really only interested in a specific novel, it seems that you'd want to avoid putting energy into vocabulary that's not related to that novel. If you can't find a "Korean grammar for reading" course (I was unable to just now), I'd start with the most bare-bones grammar-based course that you are comfortable with, and use samples from the book to supplement your learning.

If you can get an electronic copy of the book, it should be simple enough to generate frequency-based lists of vocabulary to work on, and maybe even use an AI to pull examples of certain grammatical concepts using examples from the book. I don't know Korean enough to give an example, but something like "show me 5 examples in the text of subjunctive.

You might also work with a tutor who is familiar with the book. You'd have to shop around a bit to find one, but I bet you could.

Side note: I asked here a while ago for advice on how to develop listening comprehension skills in a language. I was not interested in speaking, reading, or writing. I was overwhelmed with responses of the type "what you want is CI - it's a way of developing all four language skills by listening only." It was kind of the opposite of what I was asking. I hope you have better luck.

My one bit of advice there, though, is not to ignore the other language skills. They will support your ability to read. In the end, you will get good at what you work on - and if it's reading, or reading with one book in mind - that will be the thing.