Can't Run, Can't Hide - S2-E10
Plot hole: In the underground bunker, Nick demands to know why the vampires in Vietnam are feeding on the children "when there are so many dead up there". Yet later in this same episode (as well as at other times in the series), it's stated that "Forever Knight's" vampires can't drink from the dead. (00:20:35 - 00:27:40)
Plot hole: At the end, Nick and Schanke discuss the bruise Nick's blow supposedly left on Damir's jaw. But Nick didn't hit Damir. He grabbed and tossed him bodily into a trash heap in the alley - without ever once touching his jaw. (00:41:50)
Near Death - S2-E23
Plot hole: Dr. Linsman puts a heart monitor on Nick for the experiment, but for some bizarre reason, never questions why her "patient" has a resting heart rate of only one beat every ten minutes.
Answer: Nick was sick and tired of being an immortal bloodsucker. He wanted to be human, fall in love, get married, have children, grow old and die. As for Janette, according to her, she fell in love and the passion she felt "cured" her of her blood lust.