Scrivener does not embed fonts in ebooks, so the font used will be the one chosen by the user in the e-reader. You can use a font such as Courier to specify a monospaced font in the ebook, though.
The reason Scrivener doesn’t embed fonts, incidentally, is that it is a bit of a legal quagmire. Scrivener cannot tell which fonts installed on the computer the user has the legal right to embed in an epub file, so a feature that embedded fonts could potentially cause users to break the law without knowing it. It usually costs thousands of pounds to licence decent fonts for use in ebooks.
All the best,
Keith