In the past, we can make measurement in the 3D view when a model was displayed in CC (AT or production) It ssems this function as disapeared in the most recent version.
I was having this same problem. Turns out that it's a bug in the latest version. I assume that you are using 2 screens. If you open CC on your 'primary' screen, the measurement tool will be in it's normal place on the left side of the screen. If you open the project on your 'secondary' screen, where you probably closed it the last time you were working on it, the measurement tool is gone. Bentley knows about it and is, presumably, working to fix it in the next update.