Explanation of an AI agent requires knowledge of its design and operation. An open question is how to identify, access and use this design knowledge for generating explanations. Many AI agents used in practice, such as intelligent tutoring systems fielded in educational contexts, typically come with a User Guide that explains what the agent does, how it works and how to use the agent. However, few humans actually read the User Guide in detail. Instead, most users seek answers to their questions on demand. In this paper, we describe a question-answering agent (AskJill) that uses the User Guide for an AI-based interactive learning environment (VERA) to au- tomatically answer user’s questions and thereby explains VERA’s domain, functioning, and operation. We present a preliminary assessment of AskJill in VERA.