The Xuanming Sect was originally a very low-key sect within the Demonic Path, and the Youming Lake was a forbidden area of the Xuanming Sect, so he really didn't know much about it.
As for the Youming Lake, Senior Brother Jin actually knew even less than Meng Fan.
At least, Meng Fan knew that the Youming Lake could help cultivators in the Spirit Guiding realm break through to the Nascent Soul realm.
Chapter 198