How long do you monitor proteinuria after starting an SGLT-2 inhibitor before considering adding another medication if proteinuria is not at goal?  

I would typically wait 2-3 months. Most such patients should be on RAAS blockade which should be maximized if tolerated first. 

I think 6 months would be an appropriate answer. Each case is of course different depending on the amount of proteinuria, side effects, serum potassium levels, etc. I cannot emphasize the control of blood pressure as being a very important factor. Often this is not possible without an adequate dose ...