I have taught sight words to non-verbal children in the past. I ask them to select the word from a group. The group size depends on what level the child is at. By selecting the correct word it shows that the student knows what that word looks like and can most likely read it.
Start where the child is at. Usually a good sequence is picture/ word to picture / word match – then word match to picture/ word – then word to word – then as the previous person suggested do a drill “Give me” (the word). As in an ABA drill you can pair it with a blank card. Then another word and then a few words. Always grade up the difficulty to the student’s ability.