I asked a question on this SE. I later found out that the same question has been asked on another Q&A website. Where shall I add a link to it? In my SE question? As a comment? I don't want to copy the content as an answer to avoid license issues, and I don't want to paraphrase it. Also, new answers might be posted on the other Q&A website. I'd prefer avoid the SE community to re-writing some information that already been written somewhere else.
If you have questions like this, often if you look on the Meta site for Stack Exchange, you will find they have been answered.
In this case, answers from here can be posted on Quora with proper attribution, and vice versa, due to the type of licensing that both sites employ.
You can add the link as a comment. The goal of Stack Exchange is to exchange knowledge, and if the link points to same question, it will certainly interest future readers while avoiding potential answerers from wasting their time writing some answer whose content is already present somewhere else.