My 1st gen Kobo Glo has the following fonts pre-installed (I suppose other Kobo devices use the same set; it is possible for the user to add more but I think this is beyond the scope of your question):
Serif: (1)
Sans Serif:
Other:
Of course, these customizations are optional, and it is possible to default fonts as defined inside the ebook.
About titles, if there are not specific settings inside the ebook stylesheets, they are treated like other text: besides having a larger size, if not explicitly set to something else, the default Georgia is used.
Compared to the ereaders, the app is more limited in the customization options:
1. Including slab serif 2. I'm not really sure but I think that these are used for Chinese/Japanese languages compatibility.
Fern It's paid but the demo suits well enough for personal use
Bookerly is a serif typeface designed by Dalton Maag as an exclusive font for reading on Amazon's Kindle devices and apps.[1] Combined with a new typesetting engine, Amazon.com asserts that the font helps the user "read faster with less eyestrain."[2] The font includes ligatures and kerning pairs. [3]
Wikipedia