If your puppy has just suddenly stopped eating it could be that the puppy has just become picky and no longer likes the puppy food you're feeding it.
You might try a different brand or type of puppy food and see if your puppy starts eating again as I've had that problem as well with puppies before.
The puppy at first seemed to enjoy the food I was feeding it and then later on the puppy decided it no longer liked the puppy food and would stop eating.
I then switched the puppy food to another brand and it started eating again so that could be a cause and worth a try to switch the puppy food and see if the puppy eats again.
The puppy could also just be sick or have a medical condition that is suddenly causing the loss of appetite so if the puppy doesn't begin eating it's food again within a few days then it would be a good idea to take the puppy to the vet.
A puppy can also develop bad habits especially if you feed the puppy some of your food while eating and then the puppy will wait to get human food from it's humans and then leave the puppy food alone.
It can be nice to sometimes feed your puppy or dog some of your food but you really should not do it because it makes the puppy and dog want to just eat your food and makes them rude to other people when they come around.
The puppy or dog will then start barking at you while eating and bossing you around and bossing other people around demanding your food from you which is not a good thing.