I realise i'm being incredibly stupid but can someone provide me a step-by-step guide on how to get this working?

I created the required folder(s) within the config folder and have a guidebook in-game which i can hold in my hand but not open.

I tried to follow the instructions but clearly have done something wrong...

1.12.2 Server running on Forge.

/config/books/

/books/
books.json - contents: [ "gbook:books/rolecraft.xml" ]

/config/books/books/
rolecraft.xml

ETA:

After several restarts, but no actual changes to the guidebook files, a 'rolecraft' book finally spawned in for one of my players (but not for me) however it cannot be opened.

Since MineColonies has a guidebook, i copy/ pasted the contents exactly into my own custom book to no effect.

I have no idea what i'm doing wrong

Err, some issues with that, probably caused by my severely outdated documentation.
First, you don't need a books.json at all.
Second, you don't need a books folder inside books.

Just having config/books/rolecraft.xml should work. It certainly does for all the debug files in my development environment:

Alright, I'm just glad I've not lost the ability to follow instructions!
At work so it's going to be this evening before I can tweak the settings but I shall report back with an update :)

Ok, so the problem has not resolved.
Book at: /server_root/config/books/rolecraft.xml

gbook.cfg reads:

# Configuration file

books {
    S:GiveOnFirstJoin <
        rolecraft.xml
     >
}


general {
    # -1 for same as GUI scale, 0 for auto, 1+ for small/medium/large
    I:BookGUIScale=-1
}

rolecraft.xml contains same content as MineColonies book as before with only change being the first line which is changed to <book title="RoleCraft" cover="gbook:default" fontSize="0.6">

A book DID appear in my hotbar but cannot be opened and the book itself does not appear in JEI though the actual MineColonies book and the Guidebook do.

Also tried downgrading to 2.8.3 with no luck

Oh, uhm... yeah it won't work with the books in the server. They have to load client-side, like resource packs.

Oh ok. So how do i distribute the book to players?

Well for a datapack, the same way you distribute mod configs.
If it's a generic datapack and you just added a custom book, you can either send the users a zip file they can unpack themselves, or distribute the books as a resourcepack (I believe a server-provided resourcepack would work), in which case you will need a books.json.
For a mod (which I don't think is your situation), you'd just include it in the mod itself

Err, every time I said datapck, I meant modpack. I was discussing 1.14 stuffs on discord just now. :P

Right, i'm now more confused than ever.

I removed ALL traces from config folder(s) and created a resource pack.

Now (before trying to load the resource pack) the book has appeared in JEI bearing the correct name, and can be opened, displaying the contents of the MineColonies book, which would make sense as I had previously copy/ pasted this BUT there is no trace of the book in client or server files to edit AND trying to load the resource pack simply causes the client to freeze

Hmm I'll have to check, it could be that it's bugged, it's not often used as a feature so I don't test it regularly.
By the way are there any errors in the logs when trying to load the book from the config folder?

Not that i noticed, i'll have to have another look tomorrow. I'll remove everything guidebook-related and re-add.
Oh since it made no obvious difference i've re-upgrade to 2.9.1 again.

Since the client/ server were restarting as I typed the last reply, i quickly loaded it up and despite freezing, the resource pack HAS loaded and the demo book now appears in JEI and can be opened with the expected demo content...
As much as it makes no sense, it does seem to work but i'll look in more detail tomorrow

Welp I hope it works. If it's sometimes works sometimes doesn't, write something here and I'll give it a look.