Probably start with a good knowledge representation. Facts need to be categorized and linked to one another. I assume a solid ontology would be key. A way to p

Probably start with a good knowledge representation. Facts need to be categorized and linked to one another. I assume a solid ontology would be key. A way to process your training data to fit your knowledge graph needs to be unambiguous. No sense it teaching it anything if it becomes full of contradictions. Finding a dataset for it to learn would be tough as well. Given the breadth of possible questions, you'll need to parse huge encyclopedias and/or wikipedia. Finally, a way to efficiently query this massive amount of data. If it has to come up with an answer faster than its competitors, it better be able to lookup information pretty damn fast.