It strikes as odd that the Symbiote would drop a fragment of the Command Block under the form of a Book.

So, why not making it, through the defeat of that mini-boss?
Let me explain:

• Upon defeating the Symbiote, a cloud/orb of Command Block Particles leak out, and levitate above.
• If you throw a regular book toward it, it will be absorbed inside, similar to how the wither storm absorb blocks and items
• Some stuff happens, and the Power of the Command Block is infused inside the book!

Not only would it be more cool, but also more logical, than just a freak of nature holding some book.

maybe instead of a cloud of particles, it could just be a command block fragment or something, which is combined with a book in a crafting table.

the powers of the command block, or atleast a part of it, crystallized by high pressue after the death of the symbiont. smack that thing in an anvil and add a book to make a command block book to then make a tool! awesome idea I guess. but let's not drift off too much from the original idea this issue states so eh. sorry I guess?

while it doesn't necessarily serve a purpose,it would be a nice cosmetic

Actually, I have an idea: Y'know the patreon fbomb cosmetic? Perhaps we could have a similar effect butwith the fragment of the command block orbiting around the symbiont.Then,it could drop to the floor so that the player could get it and then combine it with a book