If you migrate to a new domain, the stats migration will be a little bit tricky.
First, get the new domain up and running with WordPress. Then, using the same API key that you used before, activate the WordPress.com Stats plugin. (Not Jetpack.) It should show you a list of other self-hosted blogs attached to your API key. Select the previous domain of your blog and complete the activation.
At this point you should be able to see your old stats in your new dashboard. If so, you can upgrade to Jetpack. If not, immediately contact WordPress.com Support. In your message to Support, include a link to this forum thread, your API key, and the new and old URLs of the blog. They will be able to help you complete the move with a minimum of lost data.