About what is the better option in this case Technically it's not wrong to use 'What about?', but it's not often used in this type of situation and sounds a bit odd What about is mostly used when asking for opinion or information What about that house? What about this color?

About what. I think, when we use "about what" it's like finishing the previous sentence as it doesn't include the details. -I talked to my teacher ( about.... ) -About what?

A) I talked to my teacher. B) About what? / What about? A) I talked to her about my assessment. Possibilities: 1. Speaker B is finishing Speaker A's incomplete sentence: I talked to my teacher... / ...ABOUT WHAT? 2. Speaker B is abbreviating his question: WHAT (did you talk to your teacher) ABOUT? You can use either in informal speech.

These are interchangeable in your example. But thee are times they would act differently: This book is about what? (what is this book about?) What about this book? (should I choose this book? - or - Does this book fit the qualities of what we are discussing?)