I think you can do it by lerping a random position.
If you're using the scrollto behaviour, create a dummy called (CamAim) object that has the scrollto behaviour.
Create another dummy object called shake.
Every random(0.2,0.8) seconds.
---> Shake, set X position to windowWidth/2+(random(-10,10))
Every random(0.2,0.8) seconds.
---> Shake, set Y position to windowHight/2+(random(-10,10))
You can replace "WindowWidth/2 & windowHight/2 with your characters XY position if or any other point where you want the camera to be center.
Then...
Every tick.
Set CamAim position X to lerp(self.X,shake.X,random(0.1,0.2))
Set CamAim position Y to lerp(self.Y,shake.Y,random(0.1,0.2))
I don't have Construct 2 in front of me now, but something like that should work,
This should create some kind of slight random movement.