WARNING: The following contains major spoilers from Star Wars: The Book of Boba Fett “Chapter 6: From the Desert Comes a Stranger,” streaming now on Disney+.
If nothing else, The Book of Boba Fett has been a series full of cameos of iconic Star Wars universe characters. Most notably, "Chapter 6: From the Desert Comes a Stranger" featured the first on-screen appearances of Luke Skywalker and Ahsoka Tano in the same scene. But did Luke and Ahsoka know each other before this?
When Ahsoka first appears in the episode, she explains to the Mandalorian that she's a "friend of the family," clearly in reference to her days with her former master, Anakin Skywalker. Later, as Luke is training with Grogu, she approaches them with the foundling armor that the Mandalorian intended to gift to his beloved Baby Yoda. Luke and Ahsoka briefly chat about Baby Yoda's training, where Luke explains that much of it has been simply reminding him of his powers. Ahsoka makes a statement that "sometimes the student guides the master," which may or may not be a nod to her own former master. Most importantly, she says to Luke "so much like your father," making her connection with the Skywalker family much more explicit. Luke doesn't seem to express surprise that Ahsoka would know his father, so it's apparent that the two may have briefly met or at the least known of each other before this meeting. However, this is not official, as there's no other canon material that addresses them knowing one another.
Of course, there are a number of ways that Luke and Ahsoka could have met, as there is plenty of overlap between their timelines. The most likely is that they made some sort of contact between the end of Return of the Jedi and the start of The Mandalorian. Ahsoka definitely knows of Luke by the time of her first on-screen debut in the second season of The Mandalorian, as she mentions that Grogu could be trained by "one of his own" in reference to Luke. However, whether or not Luke knows Ahsoka is unclear at that point.
Another likely case is that Luke and Ahsoka know one another through the Force, specifically through their relationship with Anakin Skywalker. Ahsoka was very connected with Anakin and could feel and foresee critical moments that her master experienced, such as what is seen in the final season of The Clone Wars when he makes his official turn to the dark side. Luke also experiences moments of sensing his father's presence in the original trilogy. It's entirely possible that the two simply know each other because of their strong sensitivity to the Force and how connected they were with Anakin.
As Ahsoka and Luke conclude their brief scene, Luke asks her if he will ever see her again, to which Ahsoka just replies, "Perhaps." This line of dialogue will likely become important later, as it's highly possible that the two will reconvene considering their importance to Star Wars. There's also a chance the two could have a reunion in the forthcoming Disney+ series starring Ahsoka Tano herself. While the relationship between Luke and Ahsoka is barely just being explored, there's plenty of room and possibility for future Star Wars content to provide an explanation.