Don't know why Tim Cook is accusing the figure of being plucked out of thin air
It's quite simple to figure out how they reached the figure - CNBC and others have reported it
"The European Commission used this example — based on figures from U.S. Senate public hearings — to illustrate how this worked in practice: In 2011, Apple Sales International recorded profits of €16 billion, but under the terms of the tax ruling only around €50 million were considered taxable in Ireland, leaving €15.95 billion of profits untaxed. Apple Sales International paid less than €10 million of corporate tax in Ireland in 2011 – an effective tax rate of about 0.05% on its overall annual profits. In subsequent years, Apple Sales International's profits continued to climb but, under the agreement, its taxable profits in Ireland did not — the effective tax rate decreased to 0.005% in 2014.
Only the Irish branch of Apple Sales International had the capacity to generate income from Apple products, so sales profits of the subsidiary should have been recorded in Ireland, not the home office, the Commission argues."