Через плагин portfolio for Jira, напрямую наверное никак
Нагуглил такой ответ
It´s absolutely possible. When you create the board, Jira asks you if it will be for an existing project or for an existing saved filter.
You have to select the second (first you have to create a saved filter that includes all projects you want to managed togheter, the simplest is project in (PRJ1, PRJ2, PRJ3)) and then the board, both backlog and active sprint views, will include issues from several projects.
Regards.