Have an XRF analysis done. That should pick up any silver However, I wouldn't waste your time and money. I see environmental damage, not an off composition error.
The only nickels that contain silver are the "War Nickels" that contain 35% silver. These were struck in 1942-1945 and are easily recognized by the large mintmark (P, D or S) above the dome of Monticello. Chris
There are a few 1946 nickels that were struck on war time planchets. This doesn't look anything like a silver nickel.