I have been asked this question in quiz.
I would like to ask this question from Amines Chemical Reactions topic in division Amines of Chemistry – Class 12
The best I can explain: Lower pKa value means more acidic, that is less basic, which means a higher pKb value than aniline. 4-Aminobenzoic acid can be thought of as aniline with COOH group substituted at para position. Since COOH is electron withdrawing in nature, it reduces the basic strength of aniline.