The issue is, that there's mindblowing tech all over the company, and I'd like to learn all of it. How should I think about zeroing in on a domain? Domains include Ranking, Computer Vision, NLP, Personalization, among others.
Computer Vision and NLP are both extremely hot research topics. Knowledge gained in either one is highly applicable elsewhere. If you go into NLP I recommend learning about the problems other languages pose, don't just learn NLP for English, if you can.
Personalisation is not something I can say anything about.