I have a JIRA filter which returns all the fixes in a future release:
project = MyProject AND fixVersion = \"1.1.1\" and issuetype in standardIssueTypes() and
You can install the Craftforge JQL functions https://plugins.atlassian.com/plugin/details/31601
You then create a filter
project = MyProject AND fixVersion = "1.1.1" and issuetype in standardIssueTypes() and status != Closed
Call this filter for example 'parentIssues'
Using the JQL
issue in subtaskIssuesFromFilter("parentIssues")
will retrieve all relevant subtask issues.