Be sure you have beaten the elite four, otherwise it won't work. To actually know where it is, you must first see it. It may take a while, or a short amount of time. It all depends on your luck. After you see, use you pokedex and look it up. If you click to see where it's area is, it could be on any route, or on any of the Sevii Islands.
suicune is top legendary dog just play Pokemon crystal and you'll see.
EnteiSuicuneRaikou
suicune
Raikou, Entei, and Suicune are the legendary dogs. Some consider Arcanine a legendary dog, but he is not part of the trio. the reason for this is that in an early episode, Arcanine was in the middle of a slate surrounded by Moltres, Articuno, and Zapdos. After the episode, it was decided that Arcanine was NOT a legendary dog.
entei
I've done research on this question myself and the answer is YES! After you beat the Elite Four you will be able to find the legendary dogs randomly in the grass (just like in Gold and Silver). However, for your game you will only be able to catch one of the dogs, which dog it is depends on your starter pokemon. The determiners are as follows: Starters-Legendary Dog: Bulbasaur-Entei Charmander-Suicune Squirtle-Raikou Good luck to you!
There are 3: Entei, Suicune, and Raikou
You can't. The legendary dogs didn't exist at the time yellow was released. Sorry.
Entei, Raikou and Suicine are often referred to as the Legendary Beasts or Legendary Dog pokemon. They aren't in Diamond, so you'll have to trade or migrate them. You can do this from the following games: FireRed/LeafGreen, HeartGold/SoulSilver and OmegaRuby/AlphaSapphire.
The legendary dog which you face will alway be typed to be at an advantage against your starter. Therefore, if you started with Squirtle (which becomes Blastoise), then the dog you will face is Raikou. (Bulbasaur=Entei; Charmander=Suicune)
entai- legendary dog Pokemon
lillipup