I would like to know if there is a way to create a TaskQuery to list the task that are already claimed but could have been claimed by a user that the one that is assigned ?
I would like to allow coworkers of the assigned user to claim a task if the assigned user is absent.
You can query on candidateGroup(s) which should give you the list you need. After that, you will need to filter out those that are currently "assigned" or claimed by another user.