What is the percent composition of each element in one molecule of benzoic acid (C7H6O2)?

“Percent composition” usually means percent by mass.

Mass of 1 mole of C₇H₆O₂ = (12.0×7 + 1.0×6 + 16.0×2) g = 122.0 g
Mass of C in 1 mole of C₇H₆O₂ = 12.0×7 = 84.0 g
Mass of O in 1 mole of C₇H₆O₂ = 16.0×2 = 32.0 g

Percent composition of C = (84.0/122.0) × 100% = 68.9%
Percent composition of O = (32.0/122.0) × 100% = 26.2%
Percent composition of H = 100% - (68.9% + 26.2%) = 4.9%

Percent by atoms or percent by mass? That's the first thing to clarify.