have smth at one's finger-tips/ends

(from Idioms in Speech)

to be able to repeat or use without any trouble (generally of something committed to memory); to be very familiar with something

He had all the figures, all the facts at his finger-ends. (A. Cronin)

"There's no need to despair," she said. "It may turn out very well. You've a good trade at your finger-ends that you learned before ever you thought of the Post Office." (A. Philips)