Create a layer that defines an alpha channel (transparency) for the person. Using color keying would be the best way to do this if you shot the person against a green screen.
Then use that result as a track matte (set to Alpha Inverted Matte) on a white solid layer. That will allow the text in the underlying layer to show through the part of the white solid layer that corresponds to the person.
This is a very basic compositing task, so I'm going to guess that you're new to After Effects. I strongly recommend that you begin here and work your way through the getting-started materials: