You can obtain the acknowledgement number for your PAN card application by doing one of the following:

1. Check the acknowledgement receipt provided by the PAN card agent or the NSDL/UTIITSL office, if you applied for the PAN card in person.
2. Check the email/SMS sent to you by the NSDL/UTIITSL, if you applied for the PAN card online.
3. Check the status of your PAN card application on the NSDL/UTIITSL website using your coupon number and date of birth.
4. You can also check the status of your PAN card application by calling NSDL/UTIITSL customer care.

An acknowledgement number is a 15-digit number for NSDL and a 10-digit number for UTI which is used to track the status of your PAN card application and also to make any changes to your PAN card details in future.