If your sink is equipped with an air gap drain attachment (normally it is the silver cylinder next to the faucet) this is the most likely place for a no drain issue. Remove the metal outer piece to access the plastic inner drain assembly, the top of this will also need to be removed by prying it off with a firm grasp and a back and forth motion or if it has a spherical top it will screw off. (Keep tying it will come off). Inside you will see a small opening or hose; this is the drain coming from the dishwasher and it dumps the drain water into the large hose which then goes into the disposal / drain, any obstructions to this hose and the dishwasher will only drain partially or not at all.