Donald, you probably have discovered this already, but I wanted to post this for others with new Pinnacle.
I have a Pinnacle 2016 RSQS, so not sure they're in the same place as yours. There are two shutoff valves. One is located in the cabinet beneath the stove. I had to remove the drawer below the stove to access it and it was in the far left (rear) corner. I think think once this one is open, you shouldn't have to mess with it again.
The second valve is the one beneath the sink. This is the main water supply to the water/ice dispenser. Mine was shut when I first took possession of the unit and was only able to find it after reading your post above. None of the provided manuals say anything about this valve.
The third valve you need to find is the refrigerator drain valve. Mine is located outside, beneath the refrigerator, just forward of the left front tire. When turning off the fridge, shut off the water supply beneath the sink, then open the drain valve to bleed off any water between the shutoff valve and the dispenser.
2016 Jayco 36RSQS
2015 GMC Denali 3500, dually, 4X4, Duramax diesel, 6 speed Allison transmission