Do you mean 'How do I cite the book that's being mentioned in the book that I have?'
Easy. You don't. It's not considered appropriate academic practice, if for example, you're reading Smith who then quotes a large chunk of Jones. If you want to quote that bit of Jones, you really should go back to the original source - so you need to go and find the Jones book to get that quote. However, if you just want to say that Smith mentions Jones in discussing why the Sun is hot, then you can simply say:
"Smith notes that Jones influenced his thinking that the Sun was hot (Smith 1990, pp. 10 - 11)"
