Constructed by Rayne Sperling and Gregory Schraw (1994), the Metacognitive Awareness Inventory (MAI) is a well established and useful assessment of metacogntion. The MAI has been used in hundreds of studies, ranging from basic to applied research. It is a 52-item inventory with two broad categories (i.e., knowledge of cognition and regulation of cognition), with several sub-categories.
Schraw, G., & Dennison, R. S. (1994). Assessing metacognitive awareness.Contemporary educational psychology, 19(4), 460-475.