Paul visited Jerusalem/Peter to know it.
Paul had clear reason to want to know Jesus biography.
James Dunn: “And we can also speak without exaggeration of a universal curiosity regarding the prominent or hero figure, which is as evident in ancient writings as it is today” (Note, e.g., the degree of biographical interest evident in Dio Chrysostom in the lite and teaching of Diogenes, or, on the Jewish side, in Jeremiah preserved (by his disciples) in "The Words of Jeremiah" (Jer. I.I. i.e., canonical Jeremiah).)
[See this argument and response here]