Do I need to integrate StackAI with botpress to answer free questions from knowledge base, or botpress is learning from the knowledge bases? and can answer complex questions not directly mentioned in knowledge base? Can I bend botpress answers to free questions with prompts like I do in Stack AI?

Per my understanding, Botpress performs RAG with respect to KB after understanding context of the question. Dont think it can answer question thats not mentioned in KB if your KB is based on a specific website or document. You can also change KB to Search the Web.

Thanks for your answer, So I don't need to integrate StackAI to my botpress chatbot?

Sorry I dont exactly know what StackAI is for. Botpress should be able to help you build a bot that can answer a question about a knowledge base.