Soaking liver in milk: in or out of the fridge?
Yes, you can safely soak it at room temperature, but why would you?  There's no reason not to refrigerate. 

Meat is safe for about 2 hours in the temperature danger zone of 40F/4C to 140F/60C. Beyond that, it should be cooked or refrigerated.  So, if you do decide to soak at room temperature you should cook or chill it promptly.