All of them!
If he can win RG titles until 2022, he will become the first male tennis player in the Open Era to win the same Major tournament six years in a row.
This milestone, incidentally, was achieved on the female side by Martina Navratilova, who won the Wimbledon title in that period of time, between the years 1982 to 1987.
If Nadal succeeds, it would mean he would reach his 15th Musketeers Cup and an unrealistic record of 114-2.