What if one User is using Sophos Central in several workspaces at the same time. Is one license enough or do i need one license per active session?

Hello Ardian,

Thank you for reaching out to the Sophos Community.

Regarding the workspaces, do you mean a single user has multiple devices they’re using and each of them is logged in as the same AD User? 

If this is the case, the single user (as shown in Sophos Central) will have X number of devices assigned to them. If each of the devices is actively being used, the sessions collectively will consume 1 license. 

IE: 3 Devices, one active session as "Domain\User1" on each of the devices will consume a total of 1 license. 

Sophos Central Endpoint: License usage and calculation overview
- support.sophos.com/.../KB-000035892

Licensing is per user and not per device

If a user logs into two computers using the same login credentials (e.g., domain login), there will be one user shown in Sophos Central and two associated devices.

As Qoosh said, if AD connected, using the same AD username, 1 license would be consumed.  If not AD connected, those would be detected as 3 different users.