How do teach a nonverbal child to read when the conventional way is to get the child to sound the words out?
My son was non verbal. I read everything out loud to him. We would be driving and I would read the street signs. The signs close to our house became familiar to him and one of his first words was buffalo (a street by our house). I would also read recipes, put captions on the tv and read them. Everything you read, read it out loud. By 1st grade my son was reading books like Harry Potter. He was also speaking in complete sentences.
Keep exposing them to words. For my son it clicked when we taught him words that interested him, colors. He would recognize the words in different contexts. We did just sight words for a long time and around 10 started working on phonics.