How to get SKU Number
SKU is short for Stock Keeping Unit.
It's a number you personally make up, which you yourself can use for keeping track of your applications. You can think of it as a product ID.
Source: What SKU Number to use when submitting apps?
Might be answer is late but look at Simple Information of SKU (Stock keeping unit) number is, it's an unique tracking number (an arbitrary number) that are used in appStore for your application. You can put whatever you want in there as long as it is unique among your applications. Try to follow a pattern for the SKU Number of your apps so that you will be able to better organize them. I suggest a combination of the current year + month + ID for your app. So if you’re developing your first application on september 1991 (oh,, yah it's my b'day's month and year :D ), you could put your SKU Number as “19910901”. Here, I am just suggesting you for this pattern but you can take/choose any pattern which easy for you.