N on n
The 'conference' group
These nouns refer to a meeting set up to discuss a particular thing.
In Seoul he will attend a regional conference on trade issues.
With all of these nouns except post-mortem, the preposition on is sometimes followed by an '-ing' clause.
conference congress hearing post-mortem seminar symposium
The firm will be contributing to a seminar on 'Measuring and Managing Risk' at the Law Society on 20 July.