Aside from all the other questions, such as how does an illiterate person navigate the highways and byways and safely and efficiently drive a truck, this is a pretty interesting question. The big picture answer is take night classes to learn to read, duh.
Speech to Text software is more for dictation I'm not sure it would work for this. Software for the blind comes to mind, I've worked with a blind person before and was amazed at the proficiency with which he navigated his computer. The blind-assist software was quite impressive, it would tell him exactly what was on the screen and where the cursor was. It was all keyboard input, no mouse, not sure it would work for this problem.
Is there any software that would help this person? Is there ANY way a person who cannot read will be able to perform even the most menial tasks in the near future, if not now? Most would assume janitorial work to be a pretty low barrier to entry, but even then a custodian would be expected to read the contents and safety labeling on the cleaners he or she would be using. Computer illiteracy is nearly crippling today, how much more for someone who cannot read at all...."