Any type of dog can be a service dog. The most common service dog breed is the Labrador Retriever. It also depends on the temperament of the dog. For example, you would not want a highly energetic dog who does not listen to commands to become a service dog. A dog should be properly trained and (and possibly certified) to become a service dog.

You don't approach a service dog. If you want to interact with a service dog you need to approach the handler and ask if it is ok for you to visit with their dog. They may or may not give permission.

Yes they are

In Soviet Russia, service dog needs to bring you.

The most common and well-known service dog should be Guide Dog as the first service dogs are just for the blind. However, as service dogs can also be trained to assist people with other disabilities, they gradually developed into various types, for one or more than one disability. Here are the common types of service dogs:

1. Guide dogs

2. Hearing dogs

3. Diabetic alert dogs

4. Seizure alert dogs and seizure response dogs

5. Psychiatric service dogs

6. Mobility assistance dogs

7. Autism support dogs