What is the best way to train a dog to bark on command?

same way you teach it to sit, stand etc

when he does it give him the command and the praise. he will then quickly pick up!

With my Gia I started when she was 11 weeks, showed her a treat and said "speak" and then I barked(!!), she learned almost straight away. But her mum used to do the same thing.
Val xxxx

If your dog is really playful with toys then show her a ball/toy and tease her with it keeping it out of reach. You could hide it behind your hands and show it to her in flashes to frustrate her. Be animated. Tell her to 'speak'. As soon as she barks, even once, give her the toy with loads of praise and play with her briefly. Take it off her and repeat!
Some dogs catch on straight away and some are a bit confused until the penny drops. Gradually increase the amount of barks before rewarding with the toy until she is barking steadily and readily for the toy.
If she is going to leap all over you and try and mug you for the toy then ask someone to hold her while you stand in front of her and tease her or put her on the lead and tie her to something so she can't get to you.
You can also use treats for the same thing. Frustrate her with one hidden in your hand or out of reach until she barks and then loads of praise and give her the treat.
When you give her her food bowl ask her to sit and speak before you put the food down for her. Some dogs will bark readily for their meal.
When you have a steady bark for the toy or when you can tell her the word 'speak' and she barks straight away then you are ready to move on to the 'quiet' and not before.
Sit her in front of you and tease her with the toy. Tell her to speak. When she is barking, quickly put the toy or treat out of sight in your pocket etc... Put your hand up in front of her face and give her a sharp command 'quiet', if she continues a stern No and gently hold her mouth closed. Tell her 'quiet' gently, repeat it a few times to keep her calm and then give her the reward with loads and loads of praise and a game if you use the toy.
Keep doing this a few times and she will catch on.
Alternate the reward for 'speak' and 'quiet' to keep her responses sharp. Tell her speak then quiet then speak again for the reward. Sometimes give her the reward straight away and sometimes make her speak and quiet a few times so she doesn't know when the reward is coming.
It's fun for the dogs to learn.

Lara x