Since bitcoin market runs globally 365x24x7; and it never stops. So there is no opening price and closing price.
K-line generally called yin and yang lines or candle line, these were Homma painted upright crude stick that use of daily opening price and closing price. If that day the highest price is larger than closing price or opening price, then drawn a straight line on the top of thick stick and called upper shadow, If that day the lowest price is smaller than opening price or closing price, then drawn a straight line on the bottom of thick stick and called lower shadow .
How to understand the k-line of bitcoin market on some web sites? For example: https://www.dailyfx.com/bitcoin