Main tip: If you know the exact title, or part of it in a phrase, search it "with quotation marks around it" to narrow the search results.
Here are the places librarians are likely to check for digital copies you also might want to try:
Library search (double check to see if you have the correct record, or if the records for a book could have been recently re-loaded)
If you discover what you are looking for turns out to be a book chapter (or a journal article), put in a request through ILLiad for Interlibrary Loan (ILL) to see if they can get a scanned copy. (ILL cannot get entire ebooks or scanned copies of entire print books.)
Relevant ebook databases -- (some might not have individual records in Library Search)
Google Books (sometimes the preview available includes the portion you need)
Free Library of Philadelphia Digital Media platforms (e.g. Overdrive, Hoopla, Kanopy; especially good for popular items)