participant at a conference
• (n.) One engaged with others at a banquet or merrymaking.
Sym·po'si·ast noun One engaged with others at a banquet or merrymaking. Sydney Smith. 
symposiast A participant in a symposium (a formal meeting held for the discussion of a subject, during which individual speakers may make presentations).
noun someone who participates in a symposium
a person who attends or participates in a symposium.