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.
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 Project 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.