S.F.
My daughter also had a speech delay when she was that age. I just would keep putting her on the potty and actually she was 3 1/2 before she decided that she was done with diapers and my daughter went into the bathroom and got on the toilet by herself. She didn't tell me...I went in and there she was. My daughter could say no really well so I would ask her continuously through the day if she had to go potty and she would let me know if she did or didn't....but in the beginning I would just go in and put him on the potty and at least get him familiar with the concept and then let him take his time to decide when he is going to start using it.