On this RPG, the only PL you will know is your own. Any other PL that belongs to someone else will always remain a secret. When issuing or receiving challenges, you will be sent a "Sensing" message that will tell you the kind of power your character feels from their opponent, so you can at least estimate the odds of the fight to some fashion. If your character is in possession of a Scouter, you can get an exact reading of their opponent's "Normal" or "Base" PL, but not their PL from transformations that they might have. Just keep in mind, when issuing or receiving challenges, the power your character feels or reads is based off of their opponent's "Base" PL, not their full transformed PL, whether you have a Scouter or not.
The reason PLs will be hidden is so to avoid members avoiding other members because they know they're too strong. In order to maintain an active continuity among this RPG, things must be kept random and interesting. The experience would not be that great if everyone knew everything.