This really depends on how you have your destination rule configured. If you have the "Create a Slot for each destination" enabled and you resolve your Roles and Groups, you will be able to get the users directly.

If you are using the default Plan just Once, you will get the User or Group name, after which you can use the relevant SmartObject to resolve the membership. For Roles, the UMUser SmO's "Get Role Users" method will get the membership. For Groups, use its "Get Group Users" method.

Thank you so much dc

In my case i am using (olan just once) and a Role for the destination user, Can I get the name of the exact user who currently has the task ?!

Short answer: No. The default reports will only show the Role name.

Long answer: Not out of the box, but you can create a custom component that loads this value and then uses the before-mentioned SmartObject to resolve the membership.