What's correct?

[Liquinn3]

Hi, what is correct from the question below? Thanks all. :)

¿En qué estás pensando ahora?
¿Qué estás pensando ahora?
¿A qué estás pensando ahora?

Thanks all. :)

[Rusty]

Which is correct?

Only the first one is correct.

[AngelicaDeAlquezar]

Second one can be correct too if you are asking for an opinion.
The first one is just asking where your thoughts are taking you. :)