A question about comma ... , Page 197, SC Manhattan,

[AZ679]

Manhattan SC Book, 5th Edition, page 197:

"Do not use a comma before and to separate two verbs, that have the same subject."

Sometimes, however, we have such sentences:

John ate the pizza, which was cooked by X[color=#0000FF], and later went to school.
[/color]

Here a comma comes between the subject and the second subject. Is this fine?

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On the same page:

"Wrong: Andrew and Lisa are inseparable; doing everything together."

Would that be correct to change the semicolon to comma?

Andrew and Lisa are inseparable, doing everything together.

[Everything OR Nothing]

", and later went to school " portion is wrong. ,and should be followed by an independent clause.

I think more correct version will be:

John ate the pizza, which was cooked by X, and later John went to school.

or

John ate the pizza cooked by x and later went to school .

[AZ679]

I want the relative clause to be a non-restrictive one; hence, your second suggestion is not acceptable.

But, See for example question 63 of Verbal Review, 2nd Edition: in the correct answer choice C, there is a comma between two verbs which have the same subject.

As I remember, I have seen such a comma in other questions too. I will mention them if I counter them again.

[RonPurewal]

the presence/absence of punctuation is NOT tested on this exam. if you're considering punctuation... stop, and look for some other basis for elimination.

[AZ679]

Another example that in some situations a comma can intervene two verbs of the same subject: Verbal Review, 2nd edition, # 110, correct answer choice C

Here comma precedes 'and' before the second verb of the subject of the sentence, perhaps because we have a list with 'and' before this second verb, and comma before the 'and' of the second verb is used to make the sentence more easily readable.

[AZ679]

the presence/absence of punctuation is NOT tested on this exam. if you're considering punctuation... stop, and look for some other basis for elimination.

Well, at least some answer choice can be eliminated for punctuation, e.g. for semicolon. Perhaps this is the reason Manhattan SC books includes a sub-section on punctuation rules.

[RonPurewal]

i really meant all the words that i wrote here:

the presence/absence of punctuation is NOT tested on this exam.

in other words, you will never face two answer choices that differ only in terms of whether a piece of punctuation is present.

this does NOT mean, of course, that punctuation is completely unimportant! after all, certain punctuation can prompt you to consider OTHER, RELATED issues.
e.g., in this problem, the overall structure of the sentence—of which the semicolon is only one small part—is at issue.

[RonPurewal]

similarly, you are probably well aware that 'no comma _ing' and 'comma __ing' are VERY different modifiers. still, you won't be made to choose whether the comma goes there; you just have to know what both of these modifiers do, individually.

[RonPurewal]

here is an entire page OF STUFF THAT WILL NEVER, EVER BE TESTED ON THIS EXAM:
https://writing.wisc.edu/Handbook/Commas.html

if you visit that page, remember that it's an entire page OF STUFF THAT YOU SHOULD IGNORE in preparing for this exam.
this is why i'm bothering to share the link: knowing what to ignore is just as important as knowing what to actually consider/learn/study.