In Star Trek: Nemesis, the wedding takes place on Betazed.
The wedding is that of Commander William Riker and Counselor Deanna Troi, two long-standing members of the USS Enterprise-E crew. Betazed is Troi’s homeworld, and the early scenes allow the film to show the characters in a more personal setting before the central political and military conflict begins.
Betazed is associated with telepathy in Star Trek lore. Betazoids are known for strong empathic and telepathic abilities, which explains Counselor Troi’s role as a psychological counselor and her sensitivity to the emotions of others.
The film later moves away from Betazed to confront Shinzon, the Reman leader who has taken control of Romulus. This can cause confusion with Romulus, which is the location of the film’s main political crisis, not the wedding ceremony.