How can I transfer an Ibook from Ipad to Kindle?

You can't, ebooks tend to have digital rights management on them which tie them to the store's own apps/ereaders - so ibooks from Apple can only be read in the iBooks app on an iPad, iPhone and iPod Touch.

If you own a Kindle device, you should be sure to buy all your books using the iPad's native Kindle app, and not the iBooks app. Fortunately the Kindle app is really nice.

http://www.amazon.com/gp/feature.html?ie=UTF8&docId=1000490441

You can't. Books purchased via the iBooks store are DRM protected and can't be read on a Kindle.