Default Available Search Layouts for a sObject:
Search Results: The search results that originate from searching in the left Sidebar
Search of the application or in Advanced Search.
Lookup dialogs: The lookup dialog results that originate from clicking the button
next to a lookup field on an edit page.
Tab: The list of recent records that appears on the home page of a tab, and
in related lists on other object detail pages.
Search Filter Fields: The filters that can be applied to search results.
Adding fields to Lookup dialog:
1. Go to detail page of the particular sObject, here I am going to candidates detail sObject page.
2. Click on Edit beside Lookup Dialogs shown above.
3. I added the fields to make those fields available while populating the lookup field at the edit page of the jobapplied sObject regarding to candidate record.
4. Apart form the standard field other fields also visible now by adding fields to the search list we can make the fields available.
6. Like that for other Search Layouts also we can add additional fields to visible.