How can I earn Diplomatic Victory Points?

The ways to gain and lose Diplomatic Victory points are:

Wonders:
Building the Mahabodhi Temple awards 2 Diplomatic Victory points.
Building the Potala Palace awards 1 Diplomatic Victory point.
Building the Statue of Liberty awards 4 Diplomatic Victory points.

Technologies:
Researching Seasteads, a technology of the Future Era, awards 1 Diplomatic Victory point.

Civics:
Discovering Global Warming Mitigation, a civic of the Future Era, awards 1 Diplomatic Victory point.

Competitions:
Earning the highest score in an Aid Request (or Military Aid Request) competition awards 2 Diplomatic Victory points.
Winning the first place in a non-Emergency Scored Competition awards 1 Diplomatic Victory point.

World Congress
Voting for the winning Outcome/Target combo of a World Congress Resolution awards 1 Diplomatic Victory point.
Late in the game, World Leader elections will be held during regular sessions of the World Congress. Each player can spend Diplomatic Favor to vote for one player to either gain 2 Diplomatic Victory points or lose 2 Diplomatic Victory points.

Source: https://civilization.fandom.com/wiki/Victory_(Civ6)#Diplomacy