Note- just to spell this out so that people don't misunderstand (even though the meta question here is certain that the question is really a duplicate): If your question is about how to do something that isn't part of the question post that the answer is posted to, then you should ask that in a new question post instead (make sure to search to see if that question has been asked before too). That being said...
Option: Comment on that answer asking for clarification
See /help/privileges/comment (yes- it is a privilege, so this option is not available to you if you don't have that privilege yet). It is allowed to comment with constructive criticism, which I think includes pointing out that a part of the question could use further clarification, and asking if such clarification could please be made.
Option: Place a bounty on the existing question
See /help/privileges/set-bounties. If you have the bounty privilege, set a bounty, select the "Improve details" reason, and in the custom message box, explain what details you want to be further clarified.
Maybe "by chance", someone will just come along and improve the existing answers in a way that fills your knowledge-gap, or write a new answer post that does so. /help/no-one-answers is slightly relevant to this option.
You can go and try to figure out the answer yourself through other means. Maybe there's a more specific question you can ask that fills that knowledge-gap. Maybe if you do some searching and reading on your own, you can find out the answer on your own. If you succeed, consider suggesting an edit to improve existing answer posts.
Option: Write a new question post
This option doesn't require you to have any more than 1 reputation, and it works great when the knowledge gap you have has a question in its own right (I.e. when it's not actually a duplicate question), but it's not without its flaws- namely that if you're sure it really is a duplicate, in a way, you are prompting for information fragmentation, which is what the duplicate-closure is meant to prevent (see /help/duplicate-questions). I wouldn't be surprised if the question you post gets closed, and if it doesn't get closed, and gets a good answer instead, I think the next step should be that you either edit-suggest the further clarification into the answer post in the dup-target, or write a new and improved answer post to the dup-target question.