Several developers have to work on one task.

[Эдуард Назарук]

How to set one task for two developers?
Is it possible?
Is this done through groups?

[David S. Rogers]

fastest way here is to break up the task into two tasks. be precise as to how they are different. If they are the same just requiring two people, you could duplicate the task and assign accordingly. append the task name with the developer initials. we do this as well. works fine. 

[Bill Sheboy]

Hi @Эдуард Назарук  -- Welcome to the Atlassian Community!

Why do 2 people need to be assigned to the task?  What problem are you trying to solve?

Issues in Jira can only have one assignee.  When teams need to somehow track who participated on an issue, they could add a custom user field, such as Additional Assignees, allowing adding multiple values to this other field.

Best regards,

Bill

[Эдуард Назарук]

Thank you, did as you advised.