-¿Dónde estabas a esa hora? -¿Yo? En casa.

[Tin]

How would you say this in colloquial spoken American English?

-¿Dónde estabas a esa hora?
-¿Yo? En casa.

-Y ¿dónde estaba él?
-¿Él? No lo sé.

My attempts:

A)
-Where were you at that time?
-Me? At home.

-And where was he?
-Him? I don't know.

B)
-Where were you at that time?
-I? At home.

-And where was he?
-He? I don't know.


B) sounds very wrong to me, but I'm not a native so you never know.

 

[fenixpollo]

I agree with you that (A) is the right way to express this. You would think the correct structure would use the subject pronouns (I, he), like in option B. Perhaps some of our more grammatically-inclined members know the explanation for why it's the correct option, even though it uses the object pronouns.

-Where were you at the time?
-Me? I was at home.

-And where was he?
-Him? I don't know where he was.

 

[gengo]

B) sounds very wrong to me, but I'm not a native so you never know.

Your instinct is right. B sounds unnatural, even though it is grammatically correct, because it sounds excessively formal. It makes the speaker sound pretentious and punctilious.

It is possible for A to be grammatically correct, if we assume it is an ellipsis:

-Where were you at the time?
-[Are you referring to] me? I was at home.
-And where was he?
-[Are you referring to] him? I don't know where he was.