Hello, I am really struggling with understanding "Where is here?" by Joyce Carol Oates. The story doesn't really make much sense to me, and I think...

As with so many of Joyce Carol Oates' short stories, the situation portrayed in this one features people who experience a disruption in their lives, and portrays how it changes them. This story is unusual in that it unfolds almost in real time, with the actual time expenditure of the action (the time it takes for the unexpected visitor to walk through the house) not taking much longer than it takes to read the story. This lends the story a sense of immediacy and tension, which also informs the story's underlying themes.

I think you're right to consider the themes of domestic abuse (mainly in the troubling memories stirred up in the stranger; but also the married couple seems to have some unresolved anger that is catalyzed by the stranger's visit, as they become increasingly irritable towards one another), and "not being able to go home again." That second theme is a common one in American literature, a sort of inversion of the "coming of age" theme: instead of youth's folly and hope and transformation, we get a sense of a protagonist's regret and disappointment when they see how much has changed, or remained the same. In the case of this character, "going home again" stimulates unpleasant memories. When the "mother and father" see the stranger's reaction as he looks through their home, it is as if all the things they had been denying or ignoring for years (possible discontent in their marriage?) are brought to the surface.

In that way I think the major themes of this story have to do with the ways that chance encounters can shake us from our complacency, and the ways that strangers can teach us things about ourselves, by way of reflecting emotions we cannot normally see clearly, because we're too close to them. But, true to Oates' tendency to write stories that reveal the darker side of human nature, we can also see a theme of bitterness and regret, catalyzed between the mother and father as a result of witnessing this stranger's unusual and troubling reaction to being in their home.

When the father suggests to the stranger it's time to leave because it's dinner time, he starts to cry, almost as if he is a child again and the home's current owners are surrogates for his own parents (who, it is suggested, may have mistreated him); and this moment seems to bring up more negative feelings between the mother and father as well. This suggests a further theme of a home being "haunted" by the memory of bad things that happened there, by the ghosts of those who came before, who harbor unpleasant associations; it's suggested the visitor is experiencing a somewhat haunting experience in visiting the site of his childhood trauma. The anonymous nature of the story (names are mentioned but quickly forgotten) lends a universal quality to the experience, that many readers will be able to relate to and, perhaps, find disturbing to contemplate.