Stock price when the opinion was issued
Basically the NASDAQ 100. Acts as a benchmark for a lot of people like himself. Extremely liquid. Trade, rather than invest. Top was around $550, and he thinks it will probably take out those highs before the end of the year.
Based on the look of the chart, he'd write calls against it with a strike of around $530-540. This way, you collect some premiums. If you don't want to get taken out, just keep rolling the strike price up.
QQQ vs XLK? XLK has a large position in MSFT and AAPL, whereas the QQQ is more diversified. To broaden the exposure he might add KWEB that adds exposure into the Asian marketplace, including BABA. He thinks these holdings will continue to crush things.