What's the policy for copying and pasting an answer that I wrote in one question to another, if it answers the second question, and that question has not been closed as a duplicate?
It's hard to speak of a general case. Each case should should probably be evaluated separately. But a general rule-of-thumb is that if you think exact copy-pasting will work, it might be a good idea to reanalyze why the two questions are not duplicates.
Looking at this case, if you take a closer look at the questions you will see that one question is talking about "listening" while the second seems to be focusing on "being exposed to".
The answer, on the other hand, appears to be focusing on the forbidden nature of listening.
So, at a bare-minimum, you should be analyzing whether the answer does in-fact apply to the second question. [In other words, that would be a part of your answer on the second question]
As Scimonster points out in an answer to a similar question, Mi Yodeya content, just like all Internet content, could get deleted or altered, with one of posts linked in that question being a case in point. Therefore, if you want to write an answer based on another Mi Yodeya answer, even your own, you should include sufficient actual content in the new answer to answer the present question, even if that means including the entirety of the older answer.
In addition, I endorse yydl's point that
But a general rule-of-thumb is that if you think exact copy-pasting will work, it might be a good idea to reanalyze why the two questions are not duplicates.
Make sure that the new answer is tailored to the new question, even if the difference is slight, and even if linking or copy/pasting the whole thing does a "good enough" job with much less effort.
In my case, one question was a subset of the scope of the second question, and part of the answer I gave for the second question answered the first one as well. So it made sense to me to cut and paste: