I saw someone do this in a movie many years ago. You bounce. The movie producers covered the pool's drains, thus preventing the jello from clogging the workings of the pool (pump, drain, etc) and then filled it with jello. The someone jumped into the pool off the diving board. He just bounced on the surface. It was a lot of work for such as short time on the screen.
Have you seen the movie Cloudy with a Chance of Meatballs? There is a scene in there that I think gives a fairly accurate depiction of what would happen...
I guarantee you will crash through and smack the ground!
Of course, part of the factor here is HOW MUCH jello you add to the mix... I suppose you could end up with a near cement consistency... that, of course, would also hurt!
From a height of 4 stories you would be getting close to terminal velocity. In which case while you may break the surface of the jello, you would definitely spatter and break on its surface on the way through, help more or less together by your clothing.
Off diving board might bounce but 4 stories...prolly sink