Hi @khamat_bn,
Can you check if the OSGI component - com.day.cq.workflow.impl.email.TaskEMailNotificationService is active or it is in unsatisfied state.
If it is unsatisfied, can you let know which service reference is unsatisfied.
Notification should be in AEM Inbox or as an email if mail Id is configured for the assignee.
Please check the latter case + above OSGI component status and update this thread.