I know its possible to move a person's question from worldbuilding stackexchange to meta worldbuilding stackexchange but I was trying to figure out how to migrate a question to another site on stackexchange such as philosophy stackexchange. When I was about to vote to migrate a question I noticed it seemed the only site I could vote to have it migrated to was meta worldbuilding stackexchange. Is it possible to have a question on worldbuilding stackexchange migrated to another site on stackexchange entirely such as as I said philosophy stackexchange?
If the option is not proposed to you in the closing reasons, you will need a moderator to do it. You just need to flag it (in need of a moderator intervention) with a short explanation.
I think that graduated sites can migrate their questions without mod intervention but we are not quite there yet.
First, this applies only to questions that are off-topic on Worldbuilding. If a question is on-topic here, even if it would be better somewhere else, don't migrate (or request migration) -- the person asked it here and we'll keep it.
For questions that are off-topic here but on-topic somewhere else, you can use a custom flag to suggest the migration (as Vincent said). You should also vote to close as off-topic.
Note that Stack Exchange generally discourages migrating answered questions, especially if there's an accepted answer.
When suggesting migration it's helpful to also leave a comment on the question about it. That way others have a chance to either support the suggestion or point out why it might not be a good idea. Moderators can then make use of that feedback instead of having to look up the candidate site's on-topic list and make a judgement about whether this fits. The more help you give us, the easier it is for us to make the decision to migrate (or not).