Ken Jennings was not told his Jeopardy! return would begin on the anniversary of Alex Trebek's death
The producers of the long-running trivia show shielded this information from Jennings until after filming

Yesterday, the prince of Jeopardy!, trivia champion Ken Jennings, returned to the show for another guest hosting stint. Monday, November 8, also happened to mark the one year anniversary of the death of the late Alex Trebek, but Jennings was kept in the dark on this airing detail until after filming the episode.
“Apparently, everyone was aware that we were going to air [my first episode] on the anniversary and nobody told me,” Jennings tells USA Today. “They didn’t want to put that in my head. So, I was not told until after that it was the Nov. 8 show.”
This ultimately means that yesterday’s episode did not make note of the day, with no speeches made in Trebek’s memory. However, Jennings says he had a little memento with him on stage in honor of Trebek.