You ask a very good question and there are many answers all but one is likely valid for someone (Raise the bail)
On my RV the valve was in the OUTSIDE fridge access compartment..
As someone else said under the sink.
Open the back access panel it's a louvered panel On Dometic there are slooted retangulary Thingy heads turn 90 degrees and pull out (not sure of No_Colds but think a like method).
Find the water solenoid (obvious device) and follow the line as far as you can. Then look for other access both outside and inside. Odds are it won't be far away.
Home was where I park it. but alas the.
2005 Damon Intruder 377 Alas declared a total loss
after a semi "nicked" it. Still have the radios
Kenwood TS-2000, ICOM ID-5100, ID-51A+2, ID-880 REF030C most times