I would suggest you to be read something by the USA psychologist John Flavell. He and his collaborators are leading experts in the field of metacognition or cognition about cognition.
1. Modeling forecast vs. performance outcomes? (For example, studies of the type in which participants are asked confidence in performing the next task, then noting the actual performance.) If so, this resource does a good job of walking through the list of methods folks have tried:
Article How to measure metacognition
As well, this somewhat simpler explication: https://www.ajpe.org/content/84/5/7730
2. A self-report/survey type measure to measure metacognition? A number of popular measures have been around for awhile, including MSLQ (Pintrich), MAI (metacognitive awareness inventory), and a bunch of others. One issue that would be important to consider is whether you're more interested in learning situations (e.g., students' self-awareness) or other settings.
Here's a link to a list of measures compiled by Jessica Santangelo: https://www.improvewithmetacognition.com/wp-content/uploads/2017/01/Santangelo-Metacog-Assessment-Tool-Comparison.pdf
Here's a link to MAI: https://advising.lafayette.edu/wp-content/uploads/sites/247/2021/10/metacognitive_awareness_inventory.pdf
Finally, here's a link to documentation for the MLSQ: https://eric.ed.gov/?id=ED338122