In prospect user,we have the Prospect activity. that prospect activity it creates pardot forms. Based on these Prospect activity we have to create the "Action type" under the Marketing App extension.While creating Action type one field is "Invocable Action". it is a lookup for the Invocable apex class and how can we achieve this problem?
I think you might be mixing 2 concepts.
Prospect Visitor Activity, is native to the Pardot Platform and ONLY WRITEABLE by the Pardot Platform. You could access the data from the V5 Pardot API for Visitor Activity. You could use this API, for example, from APEX which may be launched from an @InvocableMethod.
External Actions, is a means to call a Salesforce Flow or Invocable APEX from Pardot via Engagement Studio Program (ESP). Unless you are trying to "trigger" your process from an ESP, you can probably ignore this part of the platform and focus solely on the API.
Note: there is a standard component you can add to the CRM to view Prospect Activity, and Nebula Consulting has created a better & more advanced capability for this called Enhanced Engagement History. Maybe take a look before building custom?
