How do you add flag to an epic task in JIRA?
On a normal task, you just right click it and "Add flag", but when it becomes an epic you dont get that option.
Now you can flag it as Impediment (which is the default flag), see my screenshot:
We are using the Jira cloud version.
You can add a flag to an epic if it is in a sprint or on your Kanban board. Just click it like you would a normal issue, select the three dots, and "add flag". I had to create a separate Kanban board with just epics to accomplish this.
I haven't seen any built-in solutions for flag in an epic. What you can do is create a custom field and a custom filter with that field in order to take actions on the flagged items.