The legend of "The First Jedi Temple" was probably known to all (trained) Jedi, but at that point, Luke was the only Jedi left.
==

**And even Luke didn't know where it was exactly.**

Han says this in *Episode VII: The Force Awakens*:

> People that knew him best think he **went looking** for the First Jedi Temple.

The "went looking" part implies that Luke had an idea where to start, but didn't know it's exact location.

You mention a few specific people:

* **Leia** is force-sensitive, but was never "trained" as a Jedi.

* **Maz** is old and wise, and claims to *know* the Force (she is considered "Force-sensitive"), but she definitely doesn't claim to be a Jedi, or to have been trained in the force in any official capacity.

* **Kylo Ren** was trained by Luke, who might have told him about The First Jedi Temple, but since he didn't know its exact location, he wouldn't have been able to tell Kylo Ren.