So my question about this card is that while it's in play cards you control can not gain traits through card effects.

Are card effects strictly events? or does that mean stuff like The Baratheon version of The Wall wouldn't work?

Card effects is basically anything indicated by card text (and not, for instance, a game mechanic or rule stipulated in the rulebook). In this case, the Bara version of the wall would fail to grant your bara characters the Night's Watch trait while the Shadow Tower Knight was in play.

ok then can I use a Recruiter for the watch to give one of my characters the Night's Watch Trait then?

No.

Shadow Tower Knight stops anyone (including you) from using any card (event, character, location, plot, attachment, or agenda) that says something along the lines of "...gains (whatever) trait..." on a card you control. There is no secret exception.

oh ok I just wasn't sure if it just stopped constant effects or something that was targeted.

Thanks for clearing that up.