How to find a DOI
When you find an article in a library database, the DOI number will usually be included with the article's metadata or descriptive information, if one is available. (Not every article has a DOI, but participation in the DOI system is increasing, so the more recent the article, the more likely you will find a DOI.)
For example, in Academic Search Premier, the DOI appears toward the end of the description: after the title, author/s, source, subject terms, abstract, etc. You may have to scroll down to find it!
The exact location of the DOI varies by database. In some databases, you may not find a DOI in the description, but can locate it by downloading the PDF of the article:
If the DOI does not appear in the database or PDF, a third option is to search the web. You may be able to locate the article on the journal's website; even if the article is behind a paywall, its DOI may be public.
No DOI?
If no DOI is available, the MLA Handbook recommends including the permalink (or stable URL) to the database record. In Academic Search Premier, select the "Permalink" option from the Tools menu, then copy the URL that displays:
Permalinks are not as reliable as DOIs in the long run, which is why both MLA and APA citation styles now favor DOI numbers. In the absence of a DOI, APA style guidance differs somewhat from MLA; see the link below.