In this particular case it is calling the query from add-edit-postgresql, note__new (if you're using postgres, that is).
I tried to look up some documentation on the query dispatcher to post it here but couldn't find any. In case there doesn't exist one yet you might want to look at the comment at the bottom of the db api documentation page: https://openacs.org/doc/openacs-4/db-api-detailed.html.
Side note: you wrote db_exec_plsql with a 1 instead of an l ('ell') at the end - that looks like an easily overlooked error :)
Side note 2: I have a half-finished version of notes that uses ad_form and should be a better example - if anyone has time to finish it mail me (otherwise I'll do it sometime).
