Files with journal abbreviations in various subject areas are downloaded but not installed when you install EndNote. Some styles use abbreviations and others do not, if you have the full titles in your records, EndNote can automatically abbreviate them for you if you have these files installed.
When you need a journal title abbreviated but it wasn't in one of the lists provided with EndNote, you can manually add it.
If your style is supposed to use journal title abbreviations but the titles are not being abbreviated, there are two possible problems.
Edit a style to use abbreviated journal titles:
Update your bibliography to reflect style changes