Could you clarify your question? If you don't have her SIN and you are separated, you can enter 000000000. If you are being asked for her income the Canada Revenue Agency (CRA) requests you enter an estimate. You can always make an adjustment to the information at a later date.

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I have his sin but he's refusing to tell me what he made

If you do not have the exact amount, the Canada Revenue Agency suggests that you do your best to estimate the amount.  It is important to enter it because it is used to calculate certain credits that you may or may not be entitled to claim. 

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