It's a pretty broad category, and a lot of it is (still) very far from commercialization.
It's almost like asking about "the Internet" in 1992.
Here are some categories that may help to dive into...
-Natural Language Processing
AClustering vs classification in machine learning
-Neural nets (convolutional, recursive, hyerparameters and optimizTion techniques)
Read "how to create a Mind" by kurtzweil
Related (but distinct topics)
-Understand rise (and fall) of semantic web
-Relational vs NoSql databases
-distributed/parallel processing (MapReduce ->hadoop-> spark)
*edit - typo