is there a free wireless app. for Sonar Platinum using iPad Air2 ?

Not specifically for Sonar. There are a number of generic remote control apps though that will control a whole range of daws.

Also - remote apps
iTeleport app store
Teamviewer (free home version)
 
Max Arwood

Thanks Max , will check it out and get back to you . You've tested Teamviewer ( free home version ) with Sonar Platinum ?

I have used AC-7 Core HD. Works well enough, but requires some investigation and understanding, same as most things I suppose. Think was about $12 AUD?
 
I mostly use my wireless keyboard and was thinking of putting a small screen in my vocal booth that mirrors my main screen so I can see what I am doing, rather than the complexity of the above.
 
 

Splashtop Viewer emulates the whole Windows screen.

Teamviewer will work with "windows" sound device, but not all sound cards.  You will just have to test yours.
 
Max Arwood