The Project Tasks are storing in the pm_project_task table. So you can create a business rule on this table to trigger when the project tasks get inserted, updated, deleted, etc.
 
Cheers,
Tai Vu
I understood that Project tasks are storing in table 'pm_project_task'. I have created business rule for the same table already. This Business rule is working fine when you are directly making changes on the form or list of project tasks. But it is not working from Project workspace. Please refer attached snapshot.
