The spelling of the word "Innuent" appears unusual, but it is actually based on the phonetic transcription of the sound it represents. In the International Phonetic Alphabet (IPA), the symbol for the consonant cluster "nn" represents a nasal sound, similar to the "n" sound in "sing". Similarly, the "ue" in "Innuent" represents a diphthong, a combination of two vowel sounds (in this case, the "oo" and "eh" sounds). Thus, the correct pronunciation of "Innuent" would be /ɪˈnjuːɛnt/.
Significant.
Etymological and pronouncing dictionary of the English language. By Stormonth, James, Phelp, P. H. Published 1874.