That's a really good question.

If you look at page 61, you'll see that "conjugate addition" is italicized, meaning it is nice-to-know but not need-to-know.

A brief explanation. "1,2-anything" usually means something happening between two adjacent carbons. For example, 1,2-diol is two alcohol groups next to each other; C(OH)-C(OH).

By contrast, a 1,4-diol is C(OH)-C-C-C(OH).

You shouldn't need to know the precise definitions of "conjugate addition" to answer this question. Just recognize that the reaction is nucleophilic in nature (CN as a nu) and cross out C. Recognize that this is not a substitution, because there is no leaving group or anything of that nature and cross out D. You should recognize that H and CN are added onto product D and so this must be addition of some sort (compare product D versus product E to see this is true).

Then it's just a matter of logic. The H and CN are added C(H)-C(CN), which is a 1,2 arrangement. Even without knowing that notation, hopefully you'll guess that it looks more like a 1,2 than a 1,4 addition.

And if it comes to it, you've got a multiple guess between A versus B. 50% chance is better than 25%