If I ask a question in one stack site and don't get an answer, is it a good idea to ask the same question in a different stack site ?
Each site has its own strict on-topic definition. While there are some sites with overlapping definitions, this isn't all that common. It is unlikely that you can cross post a question without any changes and have it be on-topic on both sites. If you tailor it to the second site, then that's fine. Also consider making a bounty on the original question to drive more attention to it.