The best tutorials and documentation are the Apple's one :).
Core Data resource :
Core Data complete documentation
Core Data Starting Point
Core Data Tutorial for iOS
Core Data Model Editor Help
Core Data Snippets
Videos :
See the WWDC sessions, for example the 2013's sessions : 211.(Core Data Performance Optimization and Debugging) and 207. (What’s New in Core Data and iCloud)
Other tutorials :
Many tutorials in Core Data here, cocoanetics
And a special one aboute multithreading in Core Data ( how to use multiple context) Core Data Multi-Context
Books :
Best book about Core Data, in my opinion, the Marcus S. Zarra's book.
Core Data book
And also : MagicalRecord, A library that facilities the use and learning Core Data.
