Aadhar and PAN linking is mandatory. The due date for the same is extended from time to time. For non linking of aadhar to PAN there are penalties. If you wish to know if your Aadhar is linked to PAN you can check it yourself as per following process:
Step 1 - Visit Income Tax India website - https://www.incometax.gov.in/iec/foportal
Step 2 - Select "Link Aadhar Status" option. See below screenshot:
Step 3 - Enter your PAN and Aadhar Details in the next screen
Step 4 - A message will pop up showing the status of your PAN and Aadhar linking.