Is she enjoying the city she’s living in? Is he enjoying his job, his co-workers, his boss? How’s he feeling about life?
The factor that has the most explanatory power, in my view, on questions having to do with personal happiness and satisfaction in one’s personal and professional life, is the following: Is this person satisfied with their romantic relationship status?
Note I am not saying “in a happy relationship.” There are plenty of people who are single and very happy with that status. But those who are single and yet would like to be in a relationship tend to be unhappy, and project that unhappiness across all aspects of their lives. Those in unhappy relationships act similarly.
Romance rules all. To deeply understand a person and their probable happiness is to understand their romantic happenings. Of course, in almost all professional contexts, and a great deal of personal ones too, it is inappropriate to probe on such topics. Which is one reason why most friendships are not very deep.