You can enter this income as "Other Employment Income". At the bottom of this this FAQ, there are instructions on how to enter other employment income that you don't have a slip for: https://turbotax.community.intuit.ca/community/other-income/help/how-do-i-enter-other-employment-inc...

Alternatively, you could also report it as self-employment income, which would allow you to claim any expenses that you incurred while earning this income. To do this, use the “Find” (magnifying) tool to search for “self”. Select “Self-Employment” and then click the “Go” button.

This video on our YouTube channel goes through preparing a self-employed return: https://www.youtube.com/watch?v=NzszSEVEv-U