The Core Rulebook says a character must have 2 ranks of perform to become a duelist. Does anything say it has to be 2 ranks in one Perform, or could it be 1 rank each in two different performance skills?
Perform 2 ranks means 2 ranks in one perform skill -- otherwise it would say:
"Perform 1 rank, and Perform 1 rank OR Perform 2 ranks"