Audiobook
I purchased and downloaded an audiobook on my ipad but I cannot locate it to play
iPad Mini, iOS 8.3
It should have downloaded into the Music app - when you have audiobooks on an iPad you will get an Audiobooks option, possibly via the the More button, at the bottom of the Music app.
Note that audiobooks are currently a one-time only download from the store (so they won't appear in the Purchased tab for re-downloading), so you may want to copy it to your computer's iTunes via File > Devices > Transfer Purchases so that you can take a backup copy of it - it should copy over to the Books part of your iTunes library (Audiobooks if using a Mac with OS X Mavericks+ on it).