You can search for an object across all prepared sheets/models in the Project Browser.
Models exported into Autodesk Navisworks can be integrated with 2D sheets exported from the same design application to form a multi-sheet file. For example models exported from Autodesk Revit to the NWC, DWF or DWF(x) file format can be integrated with any 2D sheets exported to DWF/DWF(x) files from the same Revit project. This allows you to select a model component in the 3D environment, and then to find and review the same component in a 2D representation (such as a floor plan or section). Similarly, you can select an item in your 2D sheet and find it in the 3D model and other 2D sheets. This can enable you, for example, to quickly review a clashing item on a floor plan of the relevant system.
Preparing Sheets/Models for Searching
When you open a multi-sheet file, not all sheets/models may have been prepared to be used in Autodesk Navisworks. All sheets/models which require preparation are indicated with the Prepare 
icon in the Project Browser window. You can use the Project Browser context menu to prepare one or more sheets/models (see Sheet Browser Window, or you can prepare all sheets/models directly in the Find Items in Other Sheets and Models window. Autodesk Navisworks only searches prepared sheets/models. So if some sheets/models in your file have not been prepared, they will not be included in the search.