Does his ability to block draw of additional cards work on agendas ?

michaelius said:

Stannis' ability does not affect agenda per se. Agenda are not in play, and thus cannot be affected by other card effects. However, Stannis affects the players' ability to draw, and not the agenda's ability to let the player draw cards.

So what Stannis actually does is stop the players from drawing outside of the draw phase framework action (just to be clear, this prohibition also extends to cards drawn during the draw phase through card effects).

the1andonlime said:

Comes down to this: Agenda effects are card effects, whether they are in play or not. Stannis stops you from drawing additional cards through card effects. That means the extra cards you would be allowed for Agenda effects like Kings of Summer or Knights of the Realm are stopped by Stannis.

Thank you very much for detailed replies.