Hi Kent,
The most recent version of Adobe Photoshop Elements that will run on OS X El Capitan (10.11) is Photoshop Elements 2018.
Unfortunately, you can no longer buy this direct from Adobe, nor does Photoshop Elements 2018 appear to be available from any authorized Adobe resellers, e.g. Amazon or Best Buy.
This means you may have to resort to looking on auction sites where you will have to be very careful to ensure you are buying a legitimate license.
Hope that helps š