In Sonar, when I go to mix down audio, Sonar first says "processing audio data".  Once its done all that processing it will move on to mixing down audio.
 
So I understand that I have some audio in my project somewhere that needs to be processed.  Either I need to bounce to clips somewhere or I have some audiosnap work that has not been rendered offline etc etc.
 
So my question is:   Is there some easy way to determine what audio requires processing?  This project has over 70 tracks and I don't know what it is that Sonar needs to process before mixdown but I would like to know because I am making multiple mixes of this project and don't want to have to wait for this processing every time.  Thanks.  Hope I'm making sense.

I think you almost answered your own question. Yes things like Audio snap need to be toggled off and v vocal and I would imagine now Melodyn tracks should be bounced to track and the originals muted or archived. 
 
Corrections

Melodyne does not need to be bounced as audiosnap does.  It works seamlessly in the background.  Now with 70 audio tracks...it might be a good idea to bounce anything that has processing.

V-Vocal doesn't need to be bounced prior to Export. AFAIK, it's just AS that requires a bounce

I am curious about the OP's question as well. I was messing with Audio Snap one day on a project and saved it at some point, but did not notice till I reopened it about month later. Luckily I only had three audio tracks, so bounced all three, but I had gone through and disabled audio snap on each track. Apparently I had adjusted the audio, but like the OP I had no idea "which one." I was getting the pop-up when the project was opened, but was not sure of a way to check the tracks visually (and the inspector was saying that AS was disabled).
 
Is there a quick way to verify what clips have had AS used and mistakenly forgotten to bounce? My take-away from that experience was "always bounce" after closing AS.

I think there's a little misunderstanding here.  All audio that has had any change to it including a simple fader change will need to be processed. Of course FX will also require processing. It is only those tracks that are untouched that will not need processing. But even they will need to be mixed into a two channel audio file upon mix down. That requires processing.