So I checked with the comp rules on morph, manifest, double faced cards and face down cards and none of them seem to interact with each other to answer my question so the question is: What happens when you manifest (write into being) a double faced card (duskwatch recruiter?)
You have a 2/2 colourless, typeless etc. creature, just as if you manifest any other card. You can pay 1G to turn it into a Duskwatch Recruiter. This doesn't count as the creature entering the battlefield or transforming, so you don't get any such triggers (in case the card you manifested was, for example, a Huntmaster of the Fells - no token or life gain).
711.9. If an effect allows a player to cast a double-faced card as a face-down creature spell, or if a double-faced card enters the battlefield face down, it will have the characteristics given to it by the rule or effect that caused it to be face down. That card remains hidden, using either a face-down checklist card or opaque sleeves. See rule 707, “Face-Down Spells and Permanents.”
Manifest and double faced cards