對牛彈琴 wasted effort

對 (before) 牛 (cow) 彈 (play) 琴 (piano)

琴 can refer to other musical instruments, mostly string instruments

三角琴 grand piano

What do you suppose you are doing? Perhaps you are casting pearls before swine?

Shouldn't you save your zippy zithery music for a being who might relate to you?

Similarly, 牛耳讀經

牛 (cow) 耳 (ear) 讀 (read) 經 (classics)

Classics before cows? Or string theory. Your choice to waste.