In Jetpack Workflow, a job manager is someone who oversees and manages entire jobs - they don't necessarily have to be a People Manager within their firm. They may also manage client relationships, ensure other members on their team are moving the needle on tasks, and are generally ensuring their jobs stay on time and within budget.
By default, a job manager will have the ability to create, update or edit, delete, mark complete, duplicate, or archive jobs, but they won't be able to see all of the jobs in the firm's account. They'll also be able to create new tasks, update or modify, delete, or move complete existing tasks within jobs they can see. As for clients, they can only assign a template to a client, but they can't see all clients.
Since these are the default assignments, an owner has the ability to add or remove additional permissions for a job manager. Here's a screenshot of the default permissions assigned to someone in this role.
Related Articles: Add Staff Members, Removing Staff/User/Team Member, Edit Roles and Permissions for Staff, Staff Role, Partner Role, Owner Role