I'm not surprised to see this - 'pneumonic' for 'mnemonic' - as the people at work all pronounced it that way. (In a health care setting, and for all I know elsewhere, people have to learn keyboard shortcuts for lengthy technical terms, and the IT word for these short cuts is 'mnemonics'.)
I pronounce the p-one nyooooMONick and the mn-one nimMONick, but at the lab, both were noooMONick. That was in So Cal. The writer of the page imaged below is from London, so maybe I'm just wrong and they're both the first one.
Anyway, since it is a medical term, a story about Johnny Pneumonic would be pretty interesting. Johnny Mnemonic was about a data courier, Johnny, who has to transport double his standard 160 gigabytes of data in his brain implant to a customer in order to be given a cure for his nerve disease, whereupon Japanese gangsters get into the act. Mnemonic is from the word for the Greek personification of memory, the Titan Mnemosyne. It means to aid the memory, in particular a sequence of letters or images that help you remember. It was originally a short story by William Gibson, and made into a movie starring Keanu Reeves which I quite liked, although it was roundly panned.
'Pneumonic' just means 'pertaining to the lungs' originally from pneuma, which can either mean vital spark or breath of life, or just breath, or air, for short, and eventually refers to a 'lung'. (Not to be confused with pneumatic, which means something filled with or operated by compressed air, unless you're reading Brave New World, in which case it means bootylicious, except when describing the chairs.)
The most frequent use of the word pneumonic is in Pneumonic Plague. This is caused by the same bacterium as Black Plague or Bubonic Plague, but instead of infecting the lymphatic system (and causing it to come up in lumps, or buboes) it infects the lungs. Because it can be coughed out by the infected and inhaled by those around, it is far more infectious than flea-spread Black Plague and more virulent. At least until antibiotics were developed, it had a kill rate of close to 100%. As antibiotics fail over the next couple of decades, it could make a comeback.
If Johnny Pneumonic were to be hired to carry airborne plague across the globe, it would make a fine short story. (As 12 Monkeys already did, in fact.) You could tell Johnny he'd been infected with the cure for cancer. He'd never know the difference, at least until it was too late.