curious (about)

About is optional...yes!

I would advise writing the sentence this way:

"John was curious as to how a giraffe might appear."
or "John was curious as to what a giraffe looks like."

You can subsitute 'about' for the phrase 'as to':

"John was curious about how a giraffe might appear."
or "John was curious about what a giraffe looks like."

Thanks, Ragman.