Why would one of the forsaken not know who Slayer is? He is mentioned in the shadow's prophecies and is therefore a big deal for the shadow. I cant imagine Asmo didnt know him by sight.

He knew who his killer was. Knew that seeing his person meant his death. Died in a place and in a way that prevents the DO from transmigrating his soul to another body.

Why would his first instict at seeing a forsaken be to scream "You? NO!" Say this out loud. Go on. Say it. Kind of whisper the "You?" part and mix in a bit of disbelief. Then inhale deeply before Screaming "NO!" This is not something you would say if your first instinct was to schmooze the person standing before into sparing your life. It is something you would say if you found yourself with no way to protect yourself from what you are seeing before you. Knowing full well that what you're seeing means you are a dead man. Afterall, the blood drained from his face before he screamed. He was absolutely terrified.

If it was, as you have always believed, "spurred on by an attempt to gain time so that he could explain his predicament so that his killer might assist him" he would have started with a slight chuckle or clearing his throat and appearing very meek and subservient.