Which sentence from the following the conversation most clearly illustrates the technique of outlining a discussion plan

I would say that the sentence from this conversation (that you forgot to include here) that most clearly illustrates the technique of outlining a discussion plan is the following one:
A.Why don't we start with the symbolism of the door?
This sentence shows us that Jennifer thought about how she would start this discussion, which is obvious if you take a look at the sentences following that one. Her plan is to start with the symbolism of the door, and then move on to other moments in the story.

Conclusion is the answer