"He is in her home."
Translation:Li estas en ŝia hejmo.
Because the n ending is used for accusatives, which are not needed with the verb "estas" because estas just tells us the state of something or someone, not that someone/something is doing something to someone/something else, as in "He visits her home" (Li vizitas ŝian hejmon).
The other place where n is used is to indicate movement towards a place, as for instance, "He runs into her home" (Li kuras en ŝian domon). Without the n, "Li kuras en ŝia domo" means that he is alread in her home when he begins running.