From your question, I understand that in your task, WhatId is set to a case and now you want to set 'AssignedTo' field with 'AccountOwner' of the account of this case. If this is correct, you will need to write a trigger for this. You can check for Workflow, if that will solve the problem, your effort for writing trigger will be saved.
From your question, I understand that in your task, WhatId is set to a case and now you want to set 'AssignedTo' field with 'AccountOwner' of the account of this case. If this is correct, you will need to write a trigger for this. You can check for Workflow, if that will solve the problem, your effort for writing trigger will be saved.
Let me know if you have any specific question.
Happy to help you!
Regards,
Digamber Prasad