14 Questions per 48 Kaplan Qbank Block
It depends on what score you are aiming at.
Currently Kaplan Score Estimator is telling that you should get 71% correct in order to get 238/99 in the real exam.
71% means that you should answer 34 questions correct out of 48 blocks. Which means that you can only be wrong in 14 questions in each 48Q-Kaplan Qbank block.
However, the story might be significantly different in the case of UWorld.