Generally, this can be done with frames or with JAWS scripting. Obviously frames are easier. I am not sure if you can just get it to be read when focus is on the field, but if you create a frame then you will a prompt once the frame dimensions are marked for what you want to do. You can have it speak any time a new text is occurring. I haven't played with frames in Windows 10 which limits some of the functionality that Frames used to use, so I have no idea  how well it works with current systems.
Use jaws help for commands and search for frame to understand what is possible.
jaws-space followed by J allows you to do this.
Jonathan