I have been working with Sonar X3 Producer for a year by now, and have just upgraded to Platinum. During this year I have encountered various glitches in the 'big' PRV (not the inline one). I’ve found some of them being discussed here at the forum; I might yet report some others a bit later. For now I’d just ask a question about PRV in Multidock (I’ve checked these threads, http://forum.cakewalk.com/My-dumb-question-of-the-dayPRV-in-multidock-m2181785.aspx  and http://forum.cakewalk.com/Cant-get-PRV-in-Multidock-m2154429.aspx, but those are not my situations).
 
So, I cannot multidock my PRV at all.

1. Create a new project.
2. Insert a MIDI track.
3. Open PRV with Alt+3. The PRV occupies the entire screen below the topmost bars.
4. Click the top left corner of the PRV.
5. Select Dock in MultiDock

No reaction (selecting Enable Floating does not seem to do anything either BTW). D/Shift+D does not seem to react either. Nor double-click on a MIDI clip does  - all these actions open PRV covering the whole screen except the topmost bars.
I do remember that it used to work before on a somewhat random basis – by “random” I mean I was never quite able to figure out the rules of windows’ behavior (in sharp contrast with 8.5 where all that was entirely predictable and straight forward,  but this is another story I guess...).

Write click top area (header zone) in PRV, any VST or window you wish to add to the dock... dropdown menu...select dock.
 
I like this better as it avoids inadvertent autodocking which was frustrating in X3

Right click? Where exactly? Not sure I understand what you mean. No right click does anything for me with respect to MultiDock.
There is a drop-down menu, invokable with left click in the top left corner of the PRV window. However when I select Dock in MultiDock in there, nothing happens.

Is your Multidock visible, either at the top or bottom of the screen?

Yes, it is visible at the bottom of the screen.
Moreover, when I open Console View (via Alt+2), it immediately gets docked in the MultiDock.

So you can dock the console but not the PRV.
 
What about any of the other views: Markers, Event List, Staff View etc.
 
Can any/all of these be docked?

I can dock Console View, Markers View and Staff View.
I cannot dock PRV or Event List. With PRV, all the items on the drop down menu (Enable Floating, Dock MultiDock) are enabled but don't do anything. With Event List all these items are disabled.

What version of X3 are you on

It's Platinum; I just installed it a few days ago. Now I have both X3 Producer and Platinum on the machine, and they both exhibit the same behavior with regards to PRV.

Have you tried dragging the PRV to the top of the multidock with CTRL held down? This is new behavior in Platinum (I presume to prevent accidental docking). Hold CTRL down and drag the PRV to the top of the multidock until the blue bar appears, then release. Sorry if this is wrong, I'm not at my DAW.