What are some PhD research questions in the field of “data science process”?

I get many emails where students ask for topics of thesis or dissertation. While for a MS thesis which can be technology centric, we can provide some guidance, for PhD, it is important you find/define the question yourself, with some guidance from your advisor.
PhD involves self exploration; it provides a process to become an independent, confident researcher/innovator. Most good advisors do not give their PhD students questions (except perhaps in the first couple of years when they focus on solving targeted questions that lead to publications which may or may not become part of the dissertation), they provide an ecosystem (funding, proposals and projects which have some questions defined but have flexibility to ask more questions, research groups with ability to interact with senior and junior students and postdocs, extensive sharing of ideas and brainstorming, networking – preferably with industry, access to real-world problems and data) in which you incubate and refine your own research/innovation personna.