Jabril should do what's best for him for listen to as little outside noise as possible while making an informed decision. It's a gamble to play another season when you're an established prospect but it's also a gamble to go out early in many cases.
49 of 144 early entrants this year weren't drafted (
link). That's a lot!
He could've declared this year if he really wanted to since he's 3 years out of high school but he didn't. Maybe he wants to get his degree first. Maybe he wants to play some more on the same team as his brother. Maybe he wants to go the grad transfer route to a P5 school for the 2020 season to really try to maximize his draft status. My advice is to enjoy a talent like him while he's here.