Because you are self employed, you would use the T2125 -Part 4 - Line 9270 - Other expenses (specify) to claim your uniforms and dry cleaning expenses. Keep all receipts in case the CRA asks for them later.
This form is found under the Income tab - Self-Employment and you start from there. Make sure the top part of that form is filled out correctly, otherwise it will prevent you from Nefiling. Like dates, Industry Code, etc....