Answer
Let $p$ be the proposition that John attends a baseball game.
The expression $\neg(\neg p)$ means that John will not not attend the baseball game.
When we say something is "not not", that is a double negative, which is the same as not saying either of the "nots". Instead, we might say that John attends a baseball game, which we defined as $p$. Therefore, $p=\neg(\neg p)$
Work Step by Step
This was an explanation problem, so the explanation is given above in the answer section. When thinking about this type of question, it is helpful to put it in context of a real situation.