Box 13 is the type of currency -  If the amounts on your T5008 slip are in a foreign currency, convert them to Canadian dollars before you enter them. (Visit the Bank of Canada’s website for daily exchange rates and the average annual exchange rate).

This has come up several times in the past. 

When is Turbotax planning to add Box 13 for T5008 so USD transactions are converted at the CRA US$ rate, so every transaction does not need to be recalculated prior to entering into Turbotax?

Unfortunately, for "do-it-yourself" software such as TurboTax, you have to do the currency conversion yourself based on when yourself the securities.