How do you get live readings?

[lengster1]

Just scanned the rs and it came up clean apart from no communication between cd and head unit which i knew anyway,what block do i go into to check maf readings fats misfires etc etc Im pleased the car is tip top but hoped it would bring something up as it can come on boost a bit pulsey if you know what i mean?What cant it check? Ive serviced dvs etc,would it pick up a duff plug through the emmissions?The car is coming up its 60k service and i was wondering if a plug may of gone down probably the one thats a b%stard to change and never has been!
Thanks in advance Rich