Review the Database Reference documents that come with the product to get an understanding of how the data is organized and linked. Refiew the Adminstration Guide to get an understanding of how to modify the workflow and what data objects are available by default from which workflows. The OTA API reference will help you understand how you can access data beyond the default data objects.
The other thing to realize is that a defect can be linked to a specific executed test step, a test run, or a test instance in the Test Lab. Which of those specifically do you want to look at for defect links?
Links between defects and other entities are stored in the LINK table. You would need to look in that table at the LN_ENTITY_TYPE field to identify links to the Type of entity your interested in (i.e. test instance, test step, etc). Then you would look at the LN_ENTITY_ID to find the link record that involves the specific entity you are looking at. Once you narrow it down that far, the recordset you have should then include in the LN_BUG_ID field(s) the linked defects.
The other thing to realize is that a defect can be linked to a specific executed test step, a test run, or a test instance in the Test Lab. Which of those specifically do you want to look at for defect links?
Links between defects and other entities are stored in the LINK table. You would need to look in that table at the LN_ENTITY_TYPE field to identify links to the Type of entity your interested in (i.e. test instance, test step, etc). Then you would look at the LN_ENTITY_ID to find the link record that involves the specific entity you are looking at. Once you narrow it down that far, the recordset you have should then include in the LN_BUG_ID field(s) the linked defects.