While I was trying to think of examples for an answer to Vun-Hugh Vaw's question about voicing voiceless consonants in American English, I considered the word "acknowledge", which I think I can pronounce with [g.n] instead of with [k.n]. But I hesitated to mention it because I'm not sure if many people would agree with that judgement.
Merriam-Webster only lists "ik" and "ak" as possible pronunciations of the first syllable; the American Heritage Dictionary lists only "ak", while the OED says it can be /ək/ or /æk/ in American English.
I did a Google search of the spelling "agnowledge", and it turned up more than just a examples of this misspelling, but I'm not sure how much to read into that. I did find the following Reddit coment which is more explicit evidence for the existence of a pronunciation with voiced /g/:
Acknowledge...why do we say it like it's agnowledge?
smittyeuler Wed May 6 12:37:26 2015 UTC in AskReddit thread "What is the stupidest pronunciation of a word you've ever heard?")
Does anyone know of any more evidence about this? I'd be particularly interested in learning if any linguists have noted/discussed the occurrence of this pronunciation, but I'd also appreciate hearing about any other kinds of evidence, like a description of this pronunciation in a list of "mispronunciations to avoid".