the car is owned by my wife not myself, so attempting to do a mileage cost per km follow CRA guidance Automobile allowance rates - Canada.ca. But unable to find where to enter this in the T2125 form, please help thanks
Unlike in the US, there is no way to "claim mileage" for self-employment, rental or employment expenses. You must claim your automobile expenses based on your actual receipts and how much you used the car for work/business purposes.
The link that you have given is for employers who want to give their employees an automobile allowance that is low enough that it is not considered a taxable benefit.