Potty training

This is for the moms who work full time. Not the SAHMs. How are you guys potty training or introducing the potty? I work full time, 40/50 hours a week. My son goes to a half day preschool and they do NOT take them to the potty, but he has to be potty trained by next year in order to continue. He turned 3 on the 4th and I just dont know what to do. I got the 3 day method over the weekend and that didnt seem to work, ive tried reward system, and ive tried the cumulative reward system (6 stickers and you get a toy) and nothing seems to be clicking. If i put him on the potty he will pee (not popp) but never tells me when he wants to potty or even when he has pottied in his pullup/diaper Oh and because of this his pediatrician also mentioned he may have a cognitive delay. Which obviously being told your kid may be dumb is heartbreaking. I just dont know