Luke is presumably busy starting his doomed Jedi academy.
Cal Kestis of the video game Star Wars Jedi: Fallen Order is a candidate, though perhaps not the most likely.
Star Wars has a limited number of known living Force-users who aren’t accounted for elsewhere in the timeline at this point.
Perhaps it’s more likely that an original Jedi who hasn’t appeared in current canon yet will take on the task, or nobody will at all and Baby Yoda will just stay with Mando indefinitely.