Does ca use gross or net income to determine spousal and child support?

Neither-- depending in how you define "net". Gross is used to calculate-- the "net" is the few items deducted by dissomaster--your withheld taxes (assuming you are a W2 employee) and a very few things besides.
If you are self employed it is NOT what you'd call your "net".

Generally, it depends if you are self-employed (net income) or a wage earner (gross). Child support is determined not just by income, but also by the time the child spends with each parent, as well as other factors. You should speak with a family law attorney.

Both. Your question is vague, ambiguous, and incomplete. I suggest that you look at a child support calculator: http://www.childsup.ca.gov/resources/calculatechildsupport.aspx