To add Parent issue JQL validator, go to the transition of your workflow, switch to Validators tab and click on Add Validator button.
Select JEP - Parent Issue JQL validator and click Add button
Type the JQL that the parent issue should match to proceed the transition. Also type the message that should be displayed if the JQL does not match.
Click Add button, and that's it.
If the parent issue does not match the JQL defined above, then it does not proceed the transition and gives an error message as below.
Do not forget to publish the workflow!