In your first post, you ask if it's the total taxable income or the Net income. In your last post, you define Net income as your taxable income. Which is it?
If you are running a business, say you get total 70,000 and you spent 20,000 on supplies, you make 50,000 and this is the money you pay tax off so that is what you would list as your income for sponsorship.
If you are an employee and you get 50,000 a year and you pay taxes off that, that is what you list.
The income needed for sponsorship can be found at http://www.cic.gc.ca/english/information/applications/guides/5196E10.asp table 4.