Per the CRA; You are allowed to earn up to $38,000 in net income (excluding the amount received for the Canada Recovery Benefit), before becoming subject to the repayment provision.
Net income refers to your income as identified on line 23600 of your income tax and benefit return.
For the purpose of the Canada Recovery Benefit this includes all income earned from any source for which you would pay income tax, with the exception of benefits received for the Canada Recovery Benefit, payments from a registered disability plan, money received for the Canada Child Benefit and GST/HST credit.