I am new to unity. I have created an asset by using Blender and managed to put it in the scene. But somehow now I can only see one item at a scene. For example I can only see camera when I clicked "Main camera" at the Hierarchy toolbar. When I clicked the asset, the camera is hidden from the scene along with lighting etc. This is difficult for me since I need to put my asset in front of the camera. Where can I toggle back the views for everything in the scene?
You should have the "Gizmos" menu in the scene view, check if everything is checked there, you should also know that importing from blender will naturally downscale your objects to 0.1 of their scale, you can change that by setting scale back to 1 in the import settings.
When your objects are downscaled to the point you cannot see them if you focus on one of them you'll loose the visibility over the gizmos and vice versa.
If after checking this it is still occuring could you post the specifics of your scene setup?