All of your other recent questions have referred to 7.0 thus far, so I'll use 7 to frame my answer -
It's hard. We don't break this stuff out in any single report - you'd need to get into the Tableau logs to figure this stuf out, which is a pain.
If version 8 and greater, we include a tool call the "Performance Recorder" which essentially does what you're asking about - it breaks out the important parts of the rendering process of each sheet in a dashboard and gives you information on same.
Hope this helps!