Nikon HB-46 Bayonet Lens Hood for AF-S DX NIKKOR 35mm f/1.8G

Yes

It will. But the same Nikkor already came with a factory hood.so I ended up with an extra hood.

Do you mean what does a lens hood do or why did Nikon make it ? If the former, a lens hood is meant to reduce flare by shielding the front element from bright light sources outside the frame. It also provides a bit of shielding between the front element and the ground if the lens is dropped. If the latter.... I do think it could be a bit longer, but for the most part it's done the job for me, and I've owned the 35mm f/1.8 DX lens for almost 6 years. I bought a replacement because the original's mounting threads wore down, causing the hood to come loose unexpectedly.