I'm looking for actual documentation of the DATE_FORMAT, DATE_TRUNC, and TIMESTAMP_TRUNC functions.
Since the formulas are SQL based, they aren't all documented specifically for Domo, or if they are, I haven't seen it, lol. I'll usually Google the name of the formula and Domo, for example: DATE_FORMAT Domo, and if there is something in the knowledge base, that will turn it up. Here's an article on DATE_FORMAT
https://domo-support.domo.com/s/article/360043429953?language=en_US
When that doesn't work, I'll Google the name of the formula and SQL.
There's a button here in the formula editor to expand it:
Clicking it shows you this editor, which has a searchable function list and documentation:
There's also this support article. Though as of this writing that article does not stay up-to-date automatically with documentation changes or additions, so I'd recommend the docs in the expanded editor.