I am a member of both Quora and some Stack Exchange sites. Sometimes, I see that the same question is asked in both.
In such cases, is it OK for me to copy posts from Quora to Stack Exchange or vice-versa? Would I be violating any terms of service?
All content on Stack Exchange is licensed CC-BY-SA, so you can post any content from SE on Quora as long as you provide proper attribution. The Quora ToS grants you similar rights (Quora post) (but not exactly the same).
You remain the owner of your own content (SE and Quora are licensees), so of course, you are free to do as you wish with your content.