Assuming I have one Enemy Informer in play from a previous round, and I play a second Enemy Informer during the marshalling phase. Can I only trigger the kneel effect of the card I'm now playing or the effect of the Enemy Informer that's already in play as well?

I suspect I already know the answer but since I've seen it played both ways over OCTGN, I thought I better seek clarification on it.

When a card effect uses the name of the card, it refers only to itself. So you can't trigger the ability of the first Informer. This clarification is in the FAQ.