Tokmar was a Vulcan practice, which ancient Vulcans believed could bring lost souls back home. It involved kneeling in a meditation-like state for hours.
After learning that Spock had disappeared in 2257, Sarek immediately began practicing tokmar every day in an effort to locate him. However, he was unsuccessful as Amanda Grayson had secreted Spock within a sacred crypt containing katra stones that blocked outside telepathic links. Michael Burnham remarked she had never seen tokmar performed before this. (DIS: "Light and Shadows")
Sarek was shown performing a similar ritual on a beach in "Such Sweet Sorrow", which allowed him to make telepathic contact with Burnham.