Do different meta-cognitive measurements depend on the same mechanism? There are different meta-cognitive judgments: feeling of knowing, ratings of warmth, confidence, judgments of learning, tip-of-the-tongue or not, insight or not, etc. 

Are these judgments based on the same mechanism or there is a different mechanism in each case?
This is a topic of research currently. The short answer is no (there's quite a clear distinction between e.g. visual and memory metacognition), the long answer is that in some cases, some metacognitive mechanisms might be shared. 

Some examples for the short 'no' answer:


Patients with frontal lesions have lower visual (but not memory) metacognition than healthy controls. (http://www.ncbi.nlm.nih.gov/pubmed/25100039)
Different areas within prefrontal cortex seem to underly visual and memory metacognition see http://www.jneurosci.org/content/33/42/16657.full.pdf
There are also quite a few (older and more recent) papers within the metamemory literature, argueing that even within metamemory (i.e., in different subtypes of judgements or in semantic vs episodic memory) different mechanisms are recruited. One example here: http://www.sciencedirect.com/science/article/pii/S0028393211000182. 


Some examples showing that there actually is some degree of domain-generality:


Participants in have similar metacognitive ability in two similar visual tasks, despite different first order performance. See http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3203218/ and  http://www.pnas.org/content/108/11/4506.full
Memory (but not visual) metacognition improved after meditation training -also another form of metacognition, perhaps of the focus of attention. See http://www.ncbi.nlm.nih.gov/pubmed/24820248