Most of the BOOK is interesting.

[sitifan]

Most of +determiner+ plural/uncountable noun
https://youtu.be/l15_70dHYjg?t=191
Most of the book is interesting. Is "book" an uncountable noun?

 

[5jj]

No. The speaker is referring to a book.

 

[Tdol]

A specific book.

 

[Cunning Fox]

I'm not a teacher nor a native speaker.
I'm afraid I didn't quite understand your question. I can't think of any sentence where "book" would be uncountable. I assume the formula is just flawed, so I can't recommend relying on it. I can't give you a rule or a guidance how to go about "most of" either but have a look at a couple of examples:
- She spent most of her days in Berlin.
- He spends most of the time playing video games.
- Even though most of the book was interesting I didn't like the ending.

 

[Tarheel]

I'm neither a teacher nor a native speaker.
I'm afraid I don't quite understand your question. I can't think of any sentence where "book" would be uncountable. I assume the formula is just flawed, so I can't recommend relying on it. I can't give you a rule or a guide to using "most of" either, but have a look at a couple of examples:
- She spent most of her days in Berlin.
- He spends most of the time playing video games.
- Even though most of the book was interesting, I didn't like the ending.

Those are good examples.

 

[Tdol]

I can't think of any sentence where "book" would be uncountable

Christopher Marlowe's Dr Faustus says the following:

O would I had never seen Wittenberg, never read book


That is possibly uncountable, though it was a few hundred years ago.

 

[Phaedrus]

I can't think of any sentence where "book" would be uncountable.

Here are a few examples of sentences using "book" as a noncount noun:

Get more book for your buck!
My goodness, that's a lot of book! When do you plan on finishing it? Next spring?
In my opinion, Quirk et al. (1985) is too much book for its covers. My copy is held together by duct tape.

 

[sitifan]

Get more book for your buck!

Does the quoted sentence mean "Get more books for your money!"?

 

[Tarheel]

Maybe it's about content.

 

[Phaedrus]

Does the quoted sentence mean "Get more books for your money!"?

No. "Get more book for your buck" means "Get bigger/thicker/taller/longer/wider books for the same amount of money that you might spend elsewhere on smaller/thinner/shorter/narrower books."

 

[probus]

I would add better to Phaedrus's list.