Firstly, make sure you have the PageProof app installed in your Asana project.
Add an existing proof to an Asana task
Open the Asana task, and click the dropdown next to PageProof and select the option attach existing proof.
Copy and paste the proof URL from PageProof into the URL field (the proof name will be displayed), and click add.
The PageProof widget on the Asana task will now display up to date information about the proof.
Tip: Try creating proofs directly from tasks too.