Jira JQL to find issues which linked with Test Case through Adaptavist (Zephyr Scale) plugin

Question

I have Jira issuetype requirement and test cases which connected with requirement by Adaptavist (Zephyr Scale) plugin. I see in the Requirement issue the block "Tracebility" and list of testcases.

Please help:

1. How to write JQL to find requirement If I know Test Case key?;
2. How to find Requirement using JQL which [do not] have test cases?

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