Once Xcode 7.1 has downloaded and installed documentation (from Xcode's Preferences > Downloads) -- e.g., "iOS 91 Documentation" -- where is it located under OS X (10.11)?
Where is Xcode documentation located in OS X?
Inside Xcode. Show package contents and drill down, or use Finder's 'Go To' menu (prefixed path for your drive):
/Applications/Xcode.app/Contents/Developer/Documentation/DocSetsfor completeness
there are two places where "docsets" are in installed.
one is installed with the app /Applications/Hacks/Xcode.7.2.b.3.app/Contents/Developer/Documentation/DocSets
but this one is not a complete "docset", it only has markers, pointers to full "docset"
the actual location of the "docset" with information is here
~Library/Developer/Shared/Documentation/DocSets
if you manually download the dmg files, xcode with recognize the docsets and you can search/find but it will not update the tick boxes Preferences -> Downloads widget because you didn't grab the plist or bom file for the docset.