system
Given the following post, respond as if you're commenting on Reddit:
human
[US, HCI/Cog Sci] Starting Ph.D: How can I begin getting ideas for my dissertation?

I will be starting my Ph.D. this Fall. I've been wondering, how did you guys gain the knowledge in your field to know what was a dissertation worthy topic? How did you realize what areas needed more work? etc 

I have 2-3 months in quarantine, trying to start with my feet on the ground if possible.
gpt
This is the preliminary knowledge that your first two to three years in the program will provide. You complete advanced coursework, engage in ongoing discussions with your peers and advisors, and prepare for your qualifying exams. That's also why, in the U.S., the MA is earned after those initial exams, en route to the PhD. 

There are no shortcuts. If you're bored in quarantine, you can certainly read new (or canonical) scholarly texts in your field and start tracking some of the major debates taking place.

Congratulations on your acceptance and good luck with everything.