Most e-books do not have a DOI, however if the e-book has a DOI, include the DOI at the end of the entry. The proper way to note the DOI is to include https://doi.org/.
If there is not a publication date or if you suspect the source may be removed or altered, list the date you accessed the e-book. For example, if you access an e-book from a website and there is no publication date listed in the e-book, include "Accessed day month year" at the end of the citation. Adding the date you accessed the book (after the DOI, permalink or URL) is optional. It may be useful for your readers if the book is informal or self published and may not be available (at the link provided) at a later date.
Last Name of Author, First Name. Title. E-book ed., Publisher, year.
MLA Handbook. 9th ed., e-book ed., Modern Language Association of America, 2021.
Author's Last Name, First Name. Title of Book: Subtitle if Any. Edition if given and is not first edition, Publisher Name often shortened, Year of publication, Website Name, URL. Accessed Access Date.
Henty, George Alfred. The Cat of Bubastes: A Tale of Ancient Egypt. Blackie and Son, 1889. HathiTrust Digital Library, https://www.gutenberg.org/cache/epub/29756/pg29756-images.html. Accessed 16 November 2021.
Author's Last Name, First Name. Title of Book: Subtitle if Any. Edition if given and is not first edition, Publisher Name often shortened, Year of publication. Name of Library Database, Permalink URL.
McClean, Shilo T. Digital Storytelling: The Narrative Power of Visual Effects in Film. MIT Press, 2007. eBook Comprehensive Academic Collection (EBSCOhost), search.ebscohost.com.
Follow above formatting except only the first author listed appears in "Last Name, First Name" format. Authors' names are separated by a comma. Before the last author to be listed, add the word "and."
Last Name of First Author, First Name, and First Name Last Name of Second Author. Title of Book: Subtitle if Any, Edition if given and is not first edition, Publisher Name often shortened, Year of publication. Name of Library Database, Permalink URL.
Boss, Stephen, and Jason Cranford Teague. The New Web Typography: Create a Visual Hierarchy with Responsive Web Design, CRC Press, 2016. Ebook Central, ebookcentral.proquest.com/lib/knowledgecenter/detail.action?docID=4689429.
If you have three or more authors you may choose to list only the first author's name followed by et al. instead of listing all authors names. For example Smith, John, et al. The first author is the first name listed on the work you are citing (not the first name alphabetically).
Last Name of First Author, First Name, and First Name Last Name of Second Author. Title of Book: Subtitle if Any, Edition if given and is not first edition, Publisher Name often shortened, Year of publication. Name of Library Database.
Ziarek, Ewa Plonowska, et al. A Time for the Humanities: Futurity and the Limits of Autonomy, Fordham UP, 2008. eBook Comprehensive Academic Collection (EBSCOhost), search.ebscohost.com.