During the two years between The Force Awakens and Star Wars: The Last Jedi, fans have not only theorized about Rey's parentage or Snoke's history, but they've also had questions about other elements of the story such as the Knights of Ren. And, like most things in The Last Jedi, fans got an answer that only opens up more questions.
Warning: Spoilers for Star Wars: The Last Jedi below.
The straightforward answer to the question "where are the Knights of Ren?" is this: apparently not in The Last Jedi. Despite seeming important in The Force Awakens where Kylo Ren (Adam Driver) is joined by six intense-looking warriors in a flashback scene and Snoke (Andy Serkis) mentions them by name, the group that Kylo is supposedly the master of doesn't appear in the latest Star Wars installment. It's a bit of a letdown for fans who were hoping to find out more about this group. However, just because we didn't get to see the group and have them specifically called out as the Knights of Ren hasn't stopped two fan theories from developing that might offer some explanation as well as give fans something to look forward to in future Star Wars installments.
The first theory is that the Knights of Ren were, in fact, in The Last Jedi. They just weren't the Knights of Ren. Instead, some fans think that Snoke's Elite Praetorian Guard (the guys in the all red armor) are what the so-called Knights of Ren have become. They're certainly formidable enough when Kylo and Rey (Daisy Ridley) have to fight them after Snoke's death. And that's the major weakness in the theory. If Kylo was the Master of the Knights of Ren during The Force Awakens and the time jump between that movie and The Last Jedi is fairly short -- Kylo is still healing from the lightsaber strike to the face from The Force Awakens -- it seems unlikely that they would suddenly be serving Snoke. Also, if the Elite Praetorian Guard had previously been the Knights of Ren, it makes no sense that they'd turn on him and attack as they did when Snoke died.
The second, and probably more popular theory, is that other than the vision from The Force Awakens, we haven't seen the Knights of Ren yet, but we might have gotten an idea of the group's origin. In The Last Jedi, when we finally get the truth of what happened when Ben Solo fully turned to the Dark Side, we discover that Ben didn't kill all of Luke's students. He took several with him and while it's not explicitly said, those students might have become the Knights of Ren.
While neither of these theories give us an answer as to where the group is, one thing is certain: now that Kylo is Supreme Leader he needs some allies and maybe, just maybe, those allies will come in the form of the Knights of Ren in Episode IX.
Star Wars: The Last Jedi is in theaters now.