Finding objects in 2D
Start with the first level, in the first tab (Foundation) and go over the following tabs (Floor, Electrical, etc). Repeat the process for all the floors, with all the tabs , until you find the object.

Finding objects in 3D
If you wish to select the object in liveview, you can use the 3D selection tool (arrow icon => Live view screen) You can select items just on the active floor / tab. So, if you click on the object in live view and it doesn't become active in the plan, try with other level /tab (try all the levels independently of the level where the object seems to be)
I suggest to work with liveview / half view so you can control the plan and the live view at the same time.