RosettaCode.org has 374 submissions of different (common) problems solved using Elixir. This looks like an excellent reference and good way to contribute to our collective knowledge of programming.
There’s also the list of tasks not implemented in Elixir. So if you want more problems beyond exercism.io and Programming Elixir, there are these too 
The purpose of the project is to:
present solutions to the same task in as many different languages as possible, to demonstrate how languages are similar and different, and to aid a person with a grounding in one approach to a problem in learning another.
