The name of the JQL function is linkedIssuesInJQL.

It takes from one to three parameters:

No.TypeNameDescriptionRequired
1stringJQL queryQuery returning all linked issuesyes
2stringIssue Link typeName of the linking. All Issue Link types can be found in JIRA Administration page described in: https://confluence.atlassian.com/adminjiraserver073/configuring-issue-linking-861253998.htmloptional
3stringDirectionDirection of the linking. Can be "inward" or "outward".optional


Examples of usage:

issue in linkedIssuesInJQL("issuekey = PROJ-1")


issue in linkedIssuesInJQL("issuekey = PROJ-1", "Blocks")


issue in linkedIssuesInJQL("issuekey = PROJ-1", "Blocks", "outward")