Start with two favorite toys and teach your dog to pick them up by name, if you throw them away. Practice this in a room where there is no other toy. If your dog is not a good fetcher, use your voice, a tug-of-war or candy to reward him.
Once he knows the name of the two toys you put them both on the floor and ask to pick them up one by one. Reward correct choices with his favorite reward and continue the game. Answer wrong choices by repeating the request and possibly leading him to the right toy if he really needs help. This form of brain work is hard work for your dog, so gradually build up the vocabulary. If your dog knows the names of two toys, you can start with three.
Another way to start is to take a toy, name it and then challenge the dog to get it. Reward your dog for grabbing the toy.
Let’s say it’s a rubber toy called Ball. Hold the rubber toy in one hand and say “Ball”: let your dog take the ball and reward it. Repeat this 20 or 30 times. Then set up Ball next to a completely different toy of equal value, such as a rope toy called Rope. Say “Ball” to your dog and if your dog selects the right toy you will give a reward. If your dog does not select Ball, but the rope, then you place the rope back next to Ball. Say “Ball” again and let your dog choose. As soon as your dog is consistent in selecting Ball, you put it next to another toy. Repeat the steps until your dog always chooses Ball over other toys of equal value.
Once your dog is successful, the whole process starts again with another toy, such as the rope called “Rope”. Hold Rope up and say “Rope”, let your dog take the rope and give a reward. Repeat this 20-30 times. Then place Rope next to another toy (but not the first toy, Ball), say ‘Rope’ and only reward if your dog selects Rope. Do not say anything if he chooses the other toy, but put Rope next to the toy again and try again. Keep repeating this until you have as much success with Rope as with Ball.
Once you have established that your dog knows the names of these two toys, it is time for a test. Place Rope and Ball next to each other and ask for Ball. Reward only if your dog chooses Ball. Keep trying until your dog is successful a few times, then switch to questions for Rope. If these two things are successful, you are ready to continue the test by adding more unnamed toys. See if your dog can select from a small pile of toys Rope or Ball.