Conceptual doubt : prepositional phrases & pronoun

Dear spetznaz,
I'm happy to respond.

Unfortunately, the answer to both of your questions is "it depends." You see, you are looking for a once-and-all mathematical-type rule, and grammar doesn't work that way. Grammar is subservient to meaning, and everything about modification depends on meaning. In the larger view, the entire GMAT SC questions type concerns meaning primarily, and grammar only secondarily.

Part of what you are asking concerns the distinction of a vital vs. non-vital modifier. See these two posts:
1) That vs. Which on the GMAT
2) GMAT Grammar: Vital Noun Modifiers

If we have
. . . A of B, doing X . . .
The general pattern is that noun modifiers always touch the noun they modifier: that's the Modifier Touch Rule. Thus, "doing" would apply to B. BUT--and this is where meaning plays a crucial role--if B is a vital noun modifier of A, then these can come between a target noun and its ordinary modifier. In this case, "doing" would apply to A.

For more complicated scenarios, we would have to look at real examples of structures, examples you might find in SC practice problems. Meaning depends on context, and for questions of this sort, it doesn't make any sense to discuss grammar in the absence of meaning. Please don't post SC questions that are already posted. Search the SC part of the forum, find the questions with these kinds of modification structures, and see what the experts have to say. You are always welcome to solicit my help using the "mention this user" button.

In the bigger picture, let me caution you that it is absolutely 100% impossible to arrive at SC mastery purely by memorizing some ideal "complete" list of rules. Language is a living thing, and you have to develop intuition for it's many shifts and subtleties. See this post:
How to Improve Your GMAT Verbal Score

Does all this make sense?
Mike