Jira JQL search initiative issues

Search for issues under initiative JIRA-123:

issuekey in portfolioChildIssuesOf(JIRA-123)

Filter by issue type Story, Task, and Bug:

issuekey in portfolioChildIssuesOf(JIRA-123)
and issueType in (Story, Task, Bug)

Check the issue status is not Done or Closed:

issuekey in portfolioChildIssuesOf(JIRA-123)
and issueType in (Story, Task, Bug)
and status not in (Done, Closed)