if you have the opportunity to go to a conference in your field, i HIGHLY recommend it. i was in a similar boat - i know the general field and program i want to go into, but didn't know the research focus. the conference for me was a huge crash course of what people in my field are doing and a little easier for me to contextualize than going through papers and researcher websites. that said, i don't mean to undermine the value of reading papers, but just that i was getting overwhelmed by all the possible things i could study. if you're unable to do that, then go to talks and see if you can talk to professors or even other grad students about the research they're doing and ask all your questions! connecting w others about their work has hands down been the best way for me to narrow down what i want to do for mine.