If I want to ask an already existing and answered question, since there is something I'm not clear about in the answer, what's the best way? Just to comment (but I noticed the question isn't brought in home page), asking a new question despite being the exact same doubt, open a bounty, or something else I'm missing?
Assuming the existing question is old (> 1 month??) I would start a new question which references the existing question/answer and explain what it is about the existing answer that doesn't solve my problem.
I don't think commenting on the existing (old) answer is a good idea because the person who answered may no longer be active.