Does common stock report as a gain or loss on an income statement?

Answer 1

If you sell stock then the gain or loss from said sale is reported on Sch D. Only if you sell, though.

Answer 2

The gain or loss on sale is reported on schedule D. If the gain or loss is from a stock you have held less than one year it is short term if the stock was held more than one year it is long term.
Short term gains are taxed at you regular tax rate. Long term gians are taxed at either ten or fifteen percent depending on you gross income.