Summarize this article:

Training an adult pug requires a different approach than what you’d use with a puppy. Your adult pug may have had some previous training, but it may not have been completed or consistently reinforced. Ask the rescue group or animal shelter from where you adopted your pug about what types of additional training he will need.  Older dogs are calmer and tend to have longer attention spans than puppies.  Adult dogs are more set in their ways (including bad habits) and may take longer to train. Be patient with your adult pug during the training process. If your adult pug was mistreated by his previous owner, he may be extra sensitive to yelling or harsh punishment. As you train your adult pug, always keep a calm temper, including when he has an accident or doesn’t follow a command. If you have other household members, have them all train your adult pug. By involving everyone, your pug will feel like he’s part of your pack, which will help him feel safe and loved. To prevent him from getting confused from working with different people, make sure everyone uses the same commands, says the commands in the same tone of voice, and does not deviate from the training process (e.g., letting him get away with bad behavior).

Summary:
Identify his training needs. Be gentle with your adult pug. Involve your whole family in the training process.