CNY taking out of China

If I have 40000 CNY , do I need declare all 40000 or only 20000 ? And if declare it, what should I provide ? Do they ask me proofs from where do I have the money ? How about if my money was a gift ( donation for study from a friend ) ? How can I declare this ?

I already passed once with 23000 CNY, nobody asked me anything. This time I need pass with 42000 to pay my university. How can I declare this if this money come from friend's donation ? He isn't my legal sponsor or anything else, just a gift. Thank you!