I asked a question on this site and now I want to move this question to AskUbuntu. Should I ask this same question again there or how to migrate it. I didn't find any option to migrate.
There is no option to migrate. The best solution is to simply delete it here and then post it there. Alternatively, you can flag it for moderator attention and ask for it to be migrated. However, that means that it will keep the date it was posted on, so might not appear as new on the new site.
In general, it's simpler for everyone if you just delete it and repost.