One way is to find the dog's motivator whether it is food or toy. Then place the said motivator on the ground and hold the dog back just out of reach. Dog will try several ways to get to the object, out of frustration dog will bark, you mark and release.
Repeat many times and when dog begins to offer the bark the minute you set him up that means he now understands the game. Now you add a command to it. Change position of object, different environments, you holding it and what not. You can bring other OB into it as well, command, bark bark bark, SIT, dog sit's you release for reward. Possibilities are endless