。
Tanaka's characteristic curly hair was bouncing behind her ears.
Literal
Tanaka-san [possessive-の] characteristic curly-hair [subject-が] ear [possessive-の] behind [at-で] bouncing was.
特徴的な癖毛 ('characteristic curly hair') uses 癖毛 (くせげ, 'curly/wavy hair') — a common concern in Japanese hair culture where straight hair is the aesthetic norm. 跳ねていた ('was bouncing/flipping') uses 跳ねる for hair that sticks up or curls out. 耳の裏で ('behind the ears') is the precise location. A vivid character detail from fiction.