Although I have been photographing dogs for years without it and have done fairly well, Animal Eye-AF of the A6400 firmware 2.0 really makes things easier. This is especially true when photographing a frisky puppy. Using continuous AF with Animal Eye-AF the Sony will keep the pups eyes in focus even if the pup is moving around. The focus will follow the closest eye...
A6400, 70-200mm f/4 G OSS, 171mm, 1/60 second @ f/4, ISO 320