You may query fnd_product_installations table.
By the way, that particular patch is intended for R12.1.
If you have 12.1.3 then it can be applied straight ahead.
Go to My Oracle Support
Go Patches and Updates
Enter 'R12.AD.B.Delta.3' in the patch field
Click on the patch name
View the file name
This is the patch number: 9239089
Now run the following against EBS
select bug_number from ad_bugs where bug_number='9239089';
if a row is returned it is applied.
You can also use the OAM gui to check for applied patches
Please mark this thread as helpful or resolved if that is the case