keep your finger on the pulse翻译过来就是“将你的手指放在脉搏上”，这不就是中医的诊脉吗，通过脉搏了解病人目前的病情，所以keep your finger on the pulse引申意思就是“保持了解…的最新情况；掌握…的脉搏”。

【例句】
The situation changes daily, so you need to keep your finger on the pulse.
情况每天都在变，所以你得了解最新变化。

John has his finger on the pulse of dogs. If you have any questions about dogs, go ask him.
John对狗狗了如指掌。如果你有关于狗的任何问题，去问他。