just figuring out how the brain works: cognition/abstraction mechanisms, memory architecture, concepts/categories/context spaces, similarity, coordinates system, distributed communication, synchrony and knowledge representation in our analogue "devices".
It's an endless project but learning itself is very satisfying. We, as a species, know a whole lot about the brain, just need to digest and synthesize tons of important and scattered findings into a coherent whole.
Cognition research is in early-science stage, akin to 17th century astronomy and physics, we have many excellent & systematic data collectors, but need more Keplers, Galilei & Newtons to develop theories based on all that massive data.