The StackExchange software does not allow you to add beta sites as migration targets. Open Data is a beta site, so can't be listed as another migration target on that screen.
Regardless of what options are listed on that screen, you can always flag the question for moderator attention and suggest to moderators that they might want to consider migrating it, and you can still vote to close it as off-topic for this site.
That said, if the question is on-topic for this site, as a general rule of thumb it ordinarily should not be forcibly migrated to another site without the original poster's consent. So, if you see a question that you think is on-topic here but might get even better answers somewhere else, please don't ask the moderators to migrate it without checking with the original author first. Instead, in that situation a better approach is to post a comment mentioning the possibility of migration to the original poster and tell them how they can flag their post for migration if they want.
If the question is on-topic here, post a comment (but do not vote to close or flag for moderator attention).
If the question is off-topic here, vote to close it as off-topic. Optionally, you can flag it for moderator attention (if you think it's a good question and would be well-received at the target site), or you can post a comment letting the original author know how to do that if they choose.