Is supply of the commodity the same as stock of the commodity?

Only when economic equilibrium is reached. The supply is often not the same as the demand.

In general, both the stock and commodities exchanges are governed by a board of directors who are elected from the membership of the exchange

It's actually the other way around: the supply of a commodity influences its price, in that the more of the commodity you have, supposedly the lower the price to get people to buy more of it.

Kennametal is completely a commodities stock because the company produced a tangible item and a tangible item is considered a commmoditie in todays economy. Also, the company must first actually have...

A Trader is someone who buys/sells stocks or commodities. A Broker is one who helps the trader in his buying/selling