Charles Schwab's Shane Skinner weighs in on options trading volume amid a shortened trading week due to Thursday's market closure. In terms of gamma, Shane points to the $5900 level for the SPX as a crucial point to hold for the remainder of this week. "There's that gap from the election right near $5800 that most people have forgotten about," says Shane, who says any drift lower could fill that gap and be a sign of ferocity to the downside.