You can use the ‘flag’ link under the question, choose ‘in need of moderator intervention’, then describe the problem including which site you would like the question migrated to and why.
In general on other Stack Exchange sites, this is usually not necessary. Instead, you would choose ‘close’/‘flag’, then ‘off-topic because’ ‘This question belongs on another site in the Stack Exchange network’ and select the site from the list. Ask Different does not have any migration paths preconfigured, so a moderator is required to handle migrations manually, using the flag system described.
In terms of when to migrate though, there is an important rule of thumb:
- Don't migrate for the sake of migration. We only migrate questions because they are off-topic on the original site. It is perfectly possible for a question to be on-topic on multiple sites, but that is not a reason to migrate it elsewhere, unless the OP requests migration. As a general rule, if someone asks a question here, and it's on-topic here, it should stay here.
What is migration and how does it work?
Sometimes, though, Ask Different goes against this guideline — due to the low-traffic nature of some parts of this site, it may be beneficial to the question for it to be elsewhere. This is on a case-by-case basis and the guidelines on Meta.SE still take priority.