Josie and her mother's relationship in the episode "Culture".
The scene at the end of "Hologram" when Vaughn finally see's the Holographic message his mother has sent to him from the future. It also doubles as major character development.
Josie and Professor Z's discussion about their parents in The Movie. It's one of the few times in the series where this type of conversation doesn't come off as a Chekhov's Lecture and/or have any sugar-coating; not only are Z's words profound and eloquent, but the acting is quite good here and really helps make the scene resonate.