Do i need a dog trainer or dog behaviourist?

When it comes to your dog and getting help, you really need to look at what it is your pet needs from the problems they are portraying.

 
I.e do you need a trainer or dog behaviourist.

The differences between a dog trainer and a dog behaviourist:

A dog trainer: The teaching of a response to commands, or the performance of actions not necessarily natural to the dog, and also raising a dog accommodated to his environment by modifying natural digging, barking and eliminating behaviors. Dog training is defined as the purposeful changing of a dog's behavior.

A dog behaviourist: A dog behaviourist is a person who works in modifying or changing behavior in dogs. They can be experienced dog handlers, who have developed their experience over many years of hands-on experience, or have formal training up to degree level. Some have backgrounds in veterinary science, animal science, zoology, sociology, biology, or animal behavior, and have applied their experience and knowledge to the interaction between humans and dogs. 

 -------------------------------------------------------------------------------------------------------------------------
Basically, a dog trainer will work and train with your dog to get them to behave, over time, how you want them to e.g. to sit when asked and a dog behaviourist will look as to why your dog is behaving in the manner they are and work with your dog to stop them behaving in that manner e.g. seperation anxiety.
 -------------------------------------------------------------------------------------------------------------------------
To decide whether your dog needs either of these professionals help you need to study your dogs behaviours and see whether it is a problem or whether you just want them to be more receptive to your commands.