If you are talking about the "Analyze" that you see on the scanner's display:
When the scanner stops (or is paused) on a trunked system, you'll see "TSYS" directly above the F2 softkey
If you press F2, then you'll see Analyze directly over the F3 soft key
Press F3 to analyze the system. You may need to use the arrow/scroll keys to get to the current control channel, or to the correct system (if you started with a system other than the one you want to check).
Once on the control channel, you'll see basic system info, such as system ID, NAC (or connect tone if analog), and site number.