EndNote's search options appear on the EndNote library tool bar.
Using Quick Search
This is the default search option. Terms entered here will retrieve references from anywhere in your library.
Using the Search Panel
This enables searching on particular fields or terms, or combinations of both.
Note: You can use Search to find references you have tagged because they relate to a particular project or because you need to do something, such as quote from them or interloan the full text. Notes and Keywords has details.