Show the Project Tasks Connected to the Selected Project Name on New Task Form

Show only the Project Tasks connected to the selected Project Name by creation of new Task.

Navigate to Customization > Lists, Records, & Fields > CRM Fields > Project Task > Sourcing & Filtering subtab. 

In Filter sublist set:   

• Filter Using = Company    
• Compare Type = equal    
• Compare to Field = Project 

click Add and Save.