Link ambiguous words to their pronunciations
G121 is the linked half of the pronunciation answer. Instead of putting the pronunciation next to the word, you link the word to it, either elsewhere on the same page or on a page of its own. The link is what establishes the connection. This is the better shape when a document is thick with terms that would all need marking, since inline pronunciation on every one of them would bury the writing. W3C lists it as a sufficient technique for 3.1.6 Pronunciation, a Level AAA rule, with no conditions, and it applies to any technology that has links. We file it with the 3.1 reading and language family for the same reason we file its inline twin there.
How we find it in an audit
This is a reading pass rather than a scan. Our reviewers identify the words whose meaning turns on pronunciation, then follow each link to check that the destination actually gives the pronunciation. We check the way back too. A link that lands somewhere useful and strands the reader there has traded one problem for another.
How affected users experience it
For a screen reader user, following a link means leaving the sentence, hearing the destination, and then finding the way back to the exact word. Workable when the destination is short and the return path is obvious. Punishing when it is not. So the test is not only whether the pronunciation exists but whether reaching it costs the reader their place in the text.
Passes vs. fails
Passes
Each ambiguous word links to a short entry with a phonetic spelling and an audio clip, and a back link returns the reader to their place in the text.
Fails
A language-learning page is full of words whose meaning turns on pronunciation, with no pronunciation help anywhere.
Other ways to satisfy this rule
5 guides on this site are filed under 3.1.6 Pronunciation. W3C lists this one as sufficient for that rule on its own. Implement it correctly, in a way your readers' software actually supports, and the rule is met.
This guide is our interpretation of W3C technique G121: Linking to pronunciations. W3C publishes its techniques as guidance rather than as the standard, and says so on every one of them. The success criterion is what conformance is measured against, and a technique is one documented way to meet it.