I believe the only DAZ-produced "manual" is still the User Guide. (to my knowledge, anyway)
Hardly a complete treasure trove, it still is searchable (in PDF) and a source for basics.
(Question for anyone who knows: Is it still being updated? There's never been a date anywhere within, and searching for newer features like "volumetrics" or "ghost lighting" gets nothing, so presuming not.)
Otherwise, online tutorials and third party publications as suggested.