To access your private key, please log in to your wallet (https://wallet.portis.io).
Click on "Menu" (bottom right corner) and choose "Back-up wallet".
You will then be able to choose the wallet for which you want to view the private key.
We recommend you also write down your "Password Recovery Key" from the menu and store it in a safe place - that will allow you to recover your Portis account in case you forget your password.