It gets reported on Form 4 (Changes in Beneficial Ownership) and Form 14A (Proxy Statement).
Mr. Cook's newly vesting stock is typically sold immediately (i.e. the RSUs are settled in stock as soon as they vest and that stock is then sold), as is that of some other Apple executives (e.g. Messrs. Oppenheimer and Schiller).
In light of a rule adopted some years ago by the SEC regarding what constitutes insider trading, many executives now establish plans which specify ahead of time when, or under what circumstances, they will sell stock. That's to protect themselves from insider trading accusations. Those plans often dictate that stock is sold as soon as it vests (sometimes only enough to cover the tax implications of the vesting is sold). When we hear that a particular insider sold a large chunk of stock, often it doesn't reflect a decision recently made by that person. It's something that happened (effectively) automatically in accordance with a plan they had set up and the timing of the sale was dictated by when the RSUs happened to vest.
So, yes, Mr. Cook has received (and exercised) a number of RSU awards in recent years. But the resulting stock has, for the most part, been sold. In March he sold nearly 240,000 shares which had just vested, leaving him with the approximately 14,000 shares that he previously owned.
