How to assign single task to multi-users (Asignee)

[Sharma]

How to assign a single project task to multi-users (Asignee).

[Nic Brough -Adaptavist-]

You don't.  The assignee is the one single person responsible for an issue, and it should stay that way (because multiple assignees simply does not work in real life.  It has to be a single person with ultimate responsibility)

See https://confluence.atlassian.com/display/JIRA/How+do+I+assign+issues+to+multiple+users for the ways to indicate group involvement