Cognitive Task Analysis (CTA) interview technique is commonly used to elicit knowledge of subject-matter experts and to design instruction better focused on what experts don't know they know. However, the knowledge of how to conduct an effective interview is, itself, largely implicit. In this study we performed protocol analysis on a set of interview transcripts from an expert CTA practitioner to elicit the cognitive processes of conducting CTA interviews. We also consulted expert CTA practitioners to identify the strategies that they used during the interviews. We present key strategies that were employed by the expert CTA practitioners to ensure comprehensiveness and accuracy in the information collected, such as looking for perceptual cues (e.g. considering verbs such as "determine") to ascertain adequacy of SME's responses and selection of follow-up questions. We present a production rule model as a detailed description of the cognitive processes underlying expert CTA interviewing.