What Emotions do Dogs Appear to Respond to Most Frequently?

This article from the Journal of Veterinary Behavior, which was published in November 2017, sought to investigate what emotions dogs react to most frequently.
Examining the Emotions That Dogs Respond To
Dogs use body language to communicate their emotions. Whether it's a wagging tail or laying on their back, dogs often react to the emotions of their owners and other animals that they're familiar with. They seem to be more comfortable in some situations than others, for instance, some dogs will avoid new people if their owner doesn't say anything while others will jump up and lick the new person's face.
The Importance of Facial Expression
Researchers have found that dogs are able to recognize happiness, anger, sadness, fear, and disgust in humans. They also found that dogs are more likely to approach people who are exhibiting positive emotions.
Can Dogs Feel Disgust?
It's pretty hard to know for sure, but it appears that dogs do not physically experience disgust. A study found that unlike humans and other primates, they don't have the same anatomical features in their brain associated with this emotion. This may be because their sense of smell is about 1 million times better than human's, which means they can detect odors at such a low concentration that we can't smell at all.
Conclusion
The study found that dogs appeared to be mostly happy and content when they were pet by their owner. When the dog was pet by a stranger, they appeared scared or nervous. The same was true when the dog was pet by a family member such as an uncle or cousin. This indicates that dogs really do have emotions and respond to emotional situations just like humans do.