You would use Form T2125. There are different ways of accessing it depending on which version of TurboTax you are using.

If you're using TurboTax Online:

Click on the “Find” icon in the top right and search for “Self”. Select “Self-Employment” and then click the “Go” button.

If you're using TurboTax CD/Download:

If you are using the EasyStep Interview method, click on the “Find” icon in the blue menu. Search for “Business”. Select “Business Profile” and then click the “Go” button.

If you are using the Forms method, click on the “Forms” icon in the blue menu. Search for “T2125”. Select “T2125 B1” and then click the “OK” button.