The pope says mass daily, usually in his private chapel.
Yes, the pope can say Mass wherever he pleases.
The pope is the principal celebrant of the midnight mass on Christmas,
He celebrates Mass everyday. If he is not scheduled to say Mass at St. Peter's Basilica or St. John Lateran or at another church, he says Mass in his private chapel in the Vatican Papal Apartments.
The pope is the ruler of Vatican City (which is a country).
The Pope lives in the Vatican in Vatican City.
The Pope lives in the Vatican. In 2014 that would be Pope Francis.
Pope John XXIII called for Vatican 2.
Pope John XXIII convened the Council and Pope Paul VI made the changes to the Mass.
There is only one pope in the Vatican and that would be Pope Francis as of 2014. Pope Emeritus Benedict XVI also resides in the Vatican but has no role in governing the Church.
Vatican
Pope Paul VI closed Vatican II.
Giovanni Pierluigi da Palestrina
The Vatican in Rome is the heart of the catholic religion, that's why Rome is sometimes calles the Vatican City. The Pope lives in the vatican, who is you could say the 'head priest'.