釈迦に説法とは存じますが、医者も禁煙されたほうがよろしいのではないでしょうか。
I'm sure you don't need me to tell you this, but wouldn't it be a good idea to stop smoking?
釈迦に説法。
Don't teach fishes to swim.
釈迦に経。
You can't teach your grandmother to suck eggs.
それは釈迦に説法というもの。
That's like carrying coals to Newcastle.
8 strokes
(used phonetically)
On'Yomi: カ, ケ
Kun'Yomi:
11 strokes
explanation
On'Yomi: シャク, セキ
Kun'Yomi: とく, す.てる, ゆる.す