How do you say reading in spanish?

"reading" in Spanish is "leyendo". It is usually combined with a conjugated form of the verb "estar". "Estoy leyendo el libro" would be "I am reading the book".

This form (present progressive) is not used all that often in Spanish, at least compared with English. More often you would see "Leo el libro", which would commonly be translated as "I am reading the book."