You can submit the Proof of Ownership information here:
https://al-support.apple.com/#/al/agreement
While an employee at an Apple Store may assist you in providing this information, I have not see where they are able to unlock the device at store level anymore. That was the case long ago, but believe the process has been centralized where each store no longer has the ability to make that decision. This has just been my observation from users here who have tried at store level and I stand corrected if I am wrong. In any case, you can submit the required documentation using the link without going to an Apple Store.