You shouldn't need an automation.  You can just create a lookup field for the project from the task table.

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@BobbyNoCode wrote:

Hello, I am looking to build an automation.
I have 2 tables Task & Sub Task (Both are linked), if a sub task is created under the task record then the project selected on the task should be auto-populated on the sub task project field that's related the specific task. 
Thanks in advance!

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@BillH : Just to clarify, I already have a project lookup field on the task table, if a project is selected under the task table and after that a sub task is created under the task then the project selected in the task should be auto populated on the sub task record. 

Can't you then add a lookup in the subtask table to the task table?  I generally try to keep my bases normalized so I avoid lookups unless they're absolutely necessary, but for tools (such as Documint) I've needed to pass lookups through several levels.

Buddy, I can add a lookup to the task table from the subtask table but in that scenario task needs to selected to be able to pull the project that's selected in the task. 
I want if Task is created with a project selected then sub task is created that project name should auto populate on subtask.

I guess I'm not understanding the question.  Good luck.