While you can download and install OnSong on any device that's associated with the Apple ID of the original purchase, you can't transfer the purchase of OnSong to another Apple ID. However, if both Apple ID accounts are associated with the same credit card such as in a family, you can sign up for App Store Family Sharing. This will allow you to install OnSong on the other account free-of-charge. However, please note that a limitation with Family Sharing is that in-app purchases are not able to transfer between accounts.
I have used OnSong on a family member's Apple ID. How can I use it on my new account?
