The first thing that you need to do is to figure out what makes your dog bark. It can either be its favourite toy such as a ball or it could be a radio. Two of the most common and effective triggers are the sound of a doorbell and knocking on the door. Use whichever of the aforementioned things makes gets your dog to bark every single time.
When you show your dog it's favourite toy, turn on the radio, ring the doorbell or knock on the door and get it to start barking, say the command word “bark” or “speak” clearly.
Pat your dog and reward it with a treat in order to let it know that you are happy with its behaviour.
Do not expect a great deal from your dog. They may be smart animals, but you cannot expect their intellect to be similar to that of a human. Therefore, remain patient and repeat the second and third step for a few days. Do not forget to reward them with a treat afterwards.
After a while, stop using a trigger such as a toy, radio, doorbell or knock on the door to make the dog bark. Instead, simply use the command “speak” or “bark” to get it to start barking. Your dog would have probably become familiar with the command by now and therefore do exactly what you expect of it. Once again, show it your appreciation by patting it and giving it a treat.