There are several synonyms for the phrase "am on to" which can be used to convey a sense of understanding or realization. One such synonym is "have gotten wind of," which suggests that the speaker has become aware of something through rumors or word-of-mouth. Another option is "have caught on to," which implies that the speaker has finally understood something that was previously unclear. A similar phrase is "have figured out," which suggests that the speaker has solved a problem or mystery. "Have discovered" is another synonym that can be used when the speaker has made a new find or revelation. Overall, these synonyms for "am on to" can help to express a sense of comprehension or enlightenment.