It can be enabled by opening the Object in Edit mode and Tick the checkbox that says Allow Search
Go to this link for step by step approach :
http://www.srinivas4sfdc.com/2016/01/how-to-enable-search-layout-section-for.html
As we already know that once you have created any new custom object ,in the custom object detail page you will be seeing an section called Search Layout.But from Winter 16 releases for newly created objects you might not be able see the Search layouts section. because from winter 16 for newly created objects Search Layout Section will not be enabled automatically.Why is it?
Allow Search Feature
Salesforce has introduced a new feature in winter 16 called "Allow Search "to disable or enable Search layout for a particular custom object
By using this feature you can improve the performance of global search/Side search by excluding unnecessary custom objects from search results
At the time of custom object creation you need to choose whether you want to enable or not.
If you want enable or disable follow below steps
- Goto Setup--->Objects--->Custom Objects
- Open the custom object for which you want to enable
- Goto Search Status and select allow search to enable or deselect to disable
- Go and observe the Search Layouts section in object detail page