You can find your account number under the "Account" page in the app. Tap the icon in the top left to bring up the sidebar, select "Accounts". On this page, there will be a list of all your Trade accounts, please select the account you wish to obtain the account number for.
This will bring you to the "About this account" page which will include an account summary. You will be able to find your account number here.
Note: Your alpha-numeric account number will begin with 'H' and end in 'CAD'.