DM knows all

Allow DM to see player's whispers.  Honestly doesn't seem like it would help much as they could just switch to a third party.  However I have noticed that players try to metagame sometimes via whisper.

Assuming this is implimented what is going to stop them from just using Skype/Discord/Other chat client and evade your knowlege that way? 

This sounds like a problem that needs to be solved by talking with the players rather than requiring a fix on the platform.

@Nader,   I covered that in my opening statement.

@ Kyle  Right now it's not even an issue for me I just thought it would be nice me to see.

If you have API access (cant remember if Plus gets API) a small script could relay whatever they say to you in a GM whisper.
I use it on mine but my players know, I use it to see what they whisper other characters(in character) so they dont have to whisper it to me a second time. For example two characters working on a secret plan without the rest of the party knowing.

But to use it to spy without player knowledge goes into that ethical gray area. I can give you the code its not much at all. How you use it, or under what morals would be your decision I suppose.

man I needed that script for an old game I had that was social/political with tons of backstabbing. I would like to take you up on that offer if such a thing ever arises again and have it in my repatoire 

@dx thats actually what I'm looking for.  It's a city setting campaign, so there is a lot of what nover mentioned in the game.

I think this should work....
Without API
If you are the GM
You should be able to open up the character sheet.....go to edit
Then in the "Can be edited & controlled by" box
Just add you.
The players wont know that you did that.
and then you should be able to see all whispers. going to and fro.
But then again....it is a grey area....

This was a hot topic a few years ago that blew up into a flamefest as I should know since I was on the side of GM seeing all the whispers. I would recommend keeping this to simply a vote otherwise if this topic blows up again, this thread will get closed.

BilBo 2 said:

I think this should work....
Without API
If you are the GM
You should be able to open up the character sheet.....go to edit
Then in the "Can be edited & controlled by" box
Just add you.
The players wont know that you did that.
and then you should be able to see all whispers. going to and fro.
But then again....it is a grey area....

This works for Whispers to Character names, and is a normal function. It is something to be aware of (for the aforementioned grey area, ethical peeping reasons... If you whisper to a Character, anyone who has control of that Character will receive the Whisper).

NOTE: This is the technique that can be used to create Language (Elvish) as a "Character" to whisper to everyone who can understand Elvish.

It does not work on Whispers to Player names, under normal circumstances. These whispers are only received by the Player (absent additional hacking).

That said it can be difficult to differentiate between Player and Character in the dropdowns (sometimes using the same name). So attempting to whisper to a Player name is not an absolute prophylactic against someone else seeing it, one way or another.

If you have messages that you don't want the GM to potentially see, be sure to send in a more private format (like email) rather than entering it into your Game Creator GM's database!

Today I've collaborated with fellow Mod Team member The Aaron to clarify the statement on this in the Roll20 Wiki.
https://wiki.roll20.net/Text_Chat#Whispers