I want to display the code field in the properties of the business process, in fact the metattribue exists but I can not display it.
It requiredsto configure a 'DiagramTypeField'. This is part of DiagramType configuration.
See online documentation, section HOPEX Power Studio : Customizing Diagrams : Configuring Diagrams : Configuring a Diagram Type : Using a New MetaClass in a Diagram
This kind of configuration is used in various diagram types so it is possible that you have missed something.
I suggest you to find a similar situation in the standard product and check the related configuration.
Ex: DiagramTypeField ~03yOJScfx0a0[SHARED(FW) Operation &Cost&]
This can help you tune your own case.