When you offer somebody two slices of apple on a plate, which sentence would you choose?
Would you like some apple?
Would you like some apples?
When you offer somebody two slices of apple on a plate, which sentence would you choose?
Would you like some apple?
Would you like some apples?
"Would you like some apple?" is correct.
You are not offering the person several apples; in fact, you're offering them less than one apple (unless your slices are absurdly large).
Because of this, it is correct to use the mass noun "apple", which refers to the "stuff" an apple is made of, of which you are offering them two slices. This is because although what you are offering them is apple (ie. it has the structure, taste, chemical composition etc. which characterises apple; it is "apple-stuff"), it is not an apple (in which case you would ask them "Would you like an apple?"), and it is not several apples (in which case, grammatically, you would ask "Would you like some apples?")
Neither sentence is correct. "Would you like some apple slices?" or "Would you like a couple of apple slices?" would make more sense since you are referring to the slices.
I would say that the mass noun classification doesn't apply to the word apple. Apples are not made up of apple. They are made up of apple pulp, with an apple skin.