- Who was he?
- I think he was called Danny.
- Danny who?
- I don’t remember. Honestly.

Could I say “Danny What?” too?

Question

- Who was he?
- I think he was called Danny.
- Danny who?
- I don’t remember. Honestly.

Could I say “Danny What?” too?

Answer

It would be better to stick with “who”, because it refers to a person whereas “what” refers to a thing. People probably speak like this sometimes, but it would be considered as very informal.

Answer

"Danny what" would sound very odd to a native English speaker. "Danny Who" would be correct.

Answer

Esta es una pregunta interesante.
Depende de la situación.
Si un policía te pregunta "What is your name?"
Y dijiste "Danny".
Entonces diría "Danny what?"
(Esto significa que él está exigiendo saber su apellido.)

Pero en la mayoría de las situaciones, "Danny who" es la mejor opción.

Good luck!