The can first be found in Pandaria’s Valley of the Four Winds:

/way Valley of the Four Winds 42.4, 50.0

At 12600/21000 reputation with The Tillers you will be able to pick up, which upon completion will make join you at the Sunsong Ranch.

After moving to Draenor, follows us and sits near our Herb Garden in the Garrison.

After Legion launched, was left alone in the Garrison, until the secret was solved on how to transport him to new Dalaran. Namely, scattered throughout Dalaran there are 10 which are very difficult to see:

/way 46.15, 53.60
/way 40.40, 53.50
/way 37.47, 28.77
/way 43.99, 17.47
/way 49.15, 70.45
/way 47.55, 28.69
/way 42.73, 43.73
/way 53.92, 41.25
/way 53.30, 52.33
/way 52.01, 61.98

Loot one of these, hearthstone back to your Garrison and interact with Dog, and then he will show up in the Pet Menagerie in Dalaran.