This is the 18343rd most frequent Russian word.
щепоткой
"Щепоткой" means "a pinch" (as in a small amount, typically of a substance like salt or spices).
Here 'щепоткой' communicates sharing a small or minor part of his secret, using the term metaphorically.
Он поделился щепоткой своей тайны.
He shared a pinch of his secret.
Here, 'щепоткой' indicates a small amount of salt being added, emphasizing the size with the metaphorical meaning of a 'pinch'.
Добавь щепоткой соли в суп.
Add a pinch of salt to the soup.
In this sentence, 'щепоткой' is used figuratively to represent a small amount of patience, conveying the idea of using just a bit of an abstract quality.