I would throw the knife at him.

Being convinced you hear God's voice in you head is a sign of schizophrenia. Interesting point - how many Bible stories are really about mental health issues?

I'd tell him to fuck off.

I would tell him to fuck off!

when i was little, its those parts that made me question the bible, i remember thinking it was sad that all those other children had parents that loved someone, imaginary or not, more than them. as an adult, the idea of anyone being put before my kiddos is just laughable. you know, in an, im crazy and ill snap your tiny god neck if you touch my kids, kinda way...that kind of laughable

"Fuck off."

I'd simply tell it that any being that wanted my child to be murdered by me is not a being that is fit to worship.

Tell him to Fuck off.

I will tell him, "A benevelant god would not ask such a deed. He/she would never have created a situation in which such a deed be necessary." Then, I'd kindly bid him goodbye by saying, "Go fuck yourself, you sadistic bastard."

Get the fuck out of my face. You are an illusion.

I think in the actual story wasnt he only trying it on to see how much he was loved -( very insecure god this one )

I would say, "Go ahead and damn me then. Leave my child out of this."

Bounce his face off of a rock.

I'd be like, so you really are the asshole your believers make you out to be. Well, we've been estranged for most of my life so I'm used to it. I have nothing to gain from obeying or worshipping you because you are abusive. See ya!

Fuck you I don't need your crap.

I'd firmly indicate that unless it intended to use its power to take over my action, I'm not a puppet for it to enact its sick fantasies. Several expletives would be involved. Then I'd go about my business.

Not sure anyone could say with certainty what they would do given the line you added, "you are convinced this is God"

My initial reaction is to reject the thought experiment as it's founded on a faulty premise, but to entertain the question there would be a series of questions necessary:

Why should I sacrifice my child?
What is the reward or punishment for compliance or non-compliance?
What is the proof that you are God?
Is my child my real life child, or am I Hitler's dad?

just to name a few...

Anything appearing to me telling me sacrifice my child I would say no, be it "god" or someone with a gun to my head - the answer is no

Isn't that schizophrenia?

I'd probably chat him up a bit. Convince him to change the running water in my apartment to running wine?, and then tell him no ?about the whole killing the kid ?thing.

Flip the double bird and walk away.

I dunno. I'm trying to make this work in my head. So god appeared and in one day convinced me he was god, and that I should kill my child? I think I'd be hung up on how he'd convince me which I'm hoping would take more than one day, so we wouldn't ever get to the test (since I'm not gonna ever believe).

So if a period of time started in which I was having thoughts that god existed and was talking to me, I'd be like @VictoriaNotes and get myself to a neurologist. So again we wouldn't get very far.

So, really, not an issue for me.

It would be time to check myself into a mental institution.

My response would be one that should not like to repeat in polite company.
Abraham was a dangerous psychopath, and a God who would do that to someone so obviously mad, and then back down at the last minute for sh!ts and giggles is one evil sick messed up excremental ahole.

Straight to a&e and ask for medication

Apart from the fact that no child of mine is & no god of mine is either? should he still dare to show himself, making murderous demands - i'd kill him.