Does the Mk2 calculate SAC?

Sure, but you would think that it should be able to support such simple a commonly used metric

It does SAC Rate, RMV, and Pressure Rate numerically and graphically.

T1 obviously required to provide the data points over duration of dive.

Where are the values displayed?

I’m not using a T1 but it should be able to calculate a value like SAC without it.

Dive Log app, avg for entire dive shown bottom of Advanced Details section. Graphically, it's shown for entire dive by tapping on Dive Timeline. It stated calculations are based on tank volume set on the T1 (e.g., 11.1L).  From your watch you can change the tank volume by connecting to the T1, then scroll to dive settings, air integration, them choose the transmitter by it's name, then scroll down to tank volume. It defaults to 12L.

If your just looking for your SAC, just run the calculation using consumed volume/avg ATM/total minutes.

Cheers

The T1 is needed to provide accurate SAC rates since air consumption is one of the variables required.

In principle the Garmin Dive app could calculate SAC without a T1 transmitter if you manually enter tank size plus starting and ending pressures. However the app doesn't currently have that feature. 

True. That would be a simple workaround...